Restoring & Modifying 1971 OIF TR120

[NM Bonny]

Rudy,

*Note: the following relies on your discussion above, re: the fitment of '73-77 sliders on my '71 fork tubes or stanchions: "The stanchion o.d. is the same, the fastening to the bottom of the damper rod is the same." I was laboring under the apparently mistaken impression that they would not fit my stanchions, so I'm thrilled to be wrong.

I see from searching the web that the '73-77 disc-type slider does not have the external rib running down its length, so I'd need both sides to avoid an odd-looking front end. But it otherwise looks very similar, so the overall look of the bike would still be period-correct...

...cool. I have found a pair listed as new (but which look like good used) on eBay for far less than what a single leg sells for on the usual suspect websites--and the seller allows returns in the event I receive them and they're knackered inside. Shipping is very cheap... purchased them! (see 2nd pic)

However, I think what I'll do is ditch the Triumph hub and use the aluminum Sportster hub (I have the axle, too) shown earlier (there's room for it between the slimmer fork tubes). I'd just machine a simple adapter to position the Wilwood aluminum caliper properly to accept the 11.5" Harley-pattern rotor I already have (3rd pic), and which is considerably larger than the '73-77 Triumph rotor (by nearly 2"...?). That would stop the bike very quickly, indeed. All I'd have to do is turn down the Sporty's 3/4" axle at the outer ends to fit the Triumph sliders/retaining caps, and turn some appropriate spacer sleeves to center the hub (same as I did on the '51 FL conversion, plus a few other tricks).

The caliper adapter design would be extremely straightforward: I'd be simply moving a pair of bolt holes out from the axle in a radial dimension a smidge and adjusting the span of the outer set to fit the Wilwood caliper. I think the Performance Machine rotor has a '70s look to it with the five spoke design, and it's quite light.

Moreover, if others liked the setup, it'd easy for me to reproduce them inexpensively, as this would be a single setup operation on the big CNC mill. As with my rear disc conversion adapters for the MG Midget and Austin Healey Sprite (see 1st image), anodizing would require sufficient demand for a run of parts to make economic sense, but in a one-off prototype for my bike, just polished or painted would be fine. Polished would look cool with a black caliper...

I will adopt some of Rudy's suggested damper and sealing mods as budget permits.

Best of all, the stock sliders, axle, and conical brake will pay for much if not all of this conversion... er, well, maybe just a good chunk, as I'll now have to spring for those Borrani aluminum rims, SS spokes, and new tires...

Anyway, very exciting! Thanks again gents!

 

[Rudie]

understand correctly that all I'd have to obtain would be one L/H slider, an OEM hub and disc, and caliper (I'd prefer aluminum) to convert the suspension/wheel portion of the conversion?

Regrettably not if you wanted to use a Lockheed caliper as Triumph used - being twin opposed piston, Triumph moved the disc brake fork legs almost another inch further apart so the caliper around the inner piston cleared the wheel spokes.

I was more suggesting the the disc brake slider as possibly a better starting point for mounting the Wilwood caliper?

Otoh, if you wanted to use all Triumph parts, you could consider a complete front end from a 73 onwards disc braked OIF, that would be bolt on.

Meriden did fit Lockheed aluminium calipers as original equipment, in the last couple of years of its existence, but only in pairs on the front, and most of these had special smaller pistons, so that Meriden could fit the same 5/8" i.d. master cylinder irrespective whether a bike had twin aluminium calipers or single steel caliper.

Afaict, there are currently two versions of the "Lockheed" aluminium caliper available new:-

. CP2696-38E0 | AP Racing Back story: until 2000, Lockheed was part of Automotive Products, a components conglomerate supplying primarily British vehicle makers; AP folded in 2000, the "Lockheed" name was sold to an Indian company (according to Wikipedia); however, even during the AP days, Lockheed parts for Triumph had been handled by AP Racing, then just another AP division; when AP folded, AP Racing became a separate company (still based in the UK), is now part of Brembo.

. The "Girling" version ... Another back story: when AP were supplying Triumph with Lockheed disc brake bits, Girling was another components supplier to British vehicle makers; however, the only things the original Girling company ever supplied to Meriden were rear suspension units. At some time more recently, Wassell has acquired the rights to the "Girling" name and is using it on its pattern disc brake parts, although the parts are by definition patterns of Lockheed parts. That said, Wassell might be copying the Grimeca version of the Lockheed alloy caliper - the Grimeca version had metric internal dimensions, threads, etc. and aiui the Wassell Girling version does too.

The only downside would be being limited to what looks like a fairly small rotor.

Lockheed originally supplied 10" o.d. discs, later changing to 250 mm. However, there is at least one bolt on conversion for 12". However2, if you are only using one, it is wise to budget for a proper fork brace between the legs ...

does the T140V disc slider have the external rib running its full length that matches the T120V sliders I have?

No.

The end cap and lower casting differences are minor

Mmmm ...

As I posted earlier, the ends of the conical hub axle in the slider clamps are reduced to 9/16" (?) o.d. Otoh, the disc brake axle is not reduced from 5/8" 3/4" o.d. So it would be interesting to know what @solomon has done to his bike's conical hub slider and axle clamp to accommodate the disc brake axle's larger diameter. The aluminium axle clamps are very prone to cracking if mistreated.

 

[Rudie]

I did not see your last post until after I had posted my previous one.

*Note: the following relies on your discussion above, re: the fitment of '73-77 sliders on my '71 fork tubes or stanchions: "The stanchion o.d. is the same, the fastening to the bottom of the damper rod is the same." I was laboring under the apparently mistaken impression that they would not fit my stanchions, so I'm thrilled to be wrong.

This is true of all disc brake sliders right up to the last. Sliders from mid-79 have a different part number because of the circlip groove to retain the Leak Proof seal but they are still interchangeable with earlier.

I see from searching the web that the '73-77 disc-type slider does not have the external rib running down its length, so I'd need both sides to avoid an odd-looking front end.

Also, 'disc' slider without a caliper mounting - would have the same radius for the 5/8" 3/4" o.d. axle as the disc slider with the caliper mounting, would not have the large lug for the conical brake plate .

11.5" Harley-pattern rotor

Ime of the original standard single 10" rotor on my T160, braking hard would twist the forks - the sliders are not bushed for the stanchions but the T160 is probably(?) 50 lb heavier than a twin. Nevertheless, increased rotor o.d., consider a proper brace between the sliders? Norman Hyde does one for the disc brake forks but not for the conical hubs' - probably understandable ...

I have put twin front discs on my T160; braking hard, they just shorten the wheelbase ...

use the aluminum Sportster hub
turn down the Sporty's 3/4" axle at the outer ends to fit the Triumph sliders/retaining caps
turn some appropriate spacer sleeves to center the hub

Spacers will not be necessary to centre the hub - as with the conical hub axle and sliders, the Triumph disc brake axle has a semi-circular cross-section indentation just in from each end of the axle; the outer studs on each disc brake slider are also apart only just far enough to fit in the indentations, the axle cannot slide laterally in either direction even if the slider axle caps come loose.

 

[NM Bonny]

I did not see your last post until after I had posted my previous one.


This is true of all disc brake sliders right up to the last. Sliders from mid-79 have a different part number because of the circlip groove to retain the Leak Proof seal but they are still interchangeable with earlier.


Also, 'disc' slider without a caliper mounting - would have the same radius for the 5/8" 3/4" o.d. axle as the disc slider with the caliper mounting, would not have the large lug for the conical brake plate .


Ime of the original standard single 10" rotor on my T160, braking hard would twist the forks - the sliders are not bushed for the stanchions but the T160 is probably(?) 50 lb heavier than a twin. Nevertheless, increased rotor o.d., consider a proper brace between the sliders? Norman Hyde does one for the disc brake forks but not for the conical hubs' - probably understandable ...

I have put twin front discs on my T160; braking hard, they just shorten the wheelbase ...


Spacers will not be necessary to centre the hub - as with the conical hub axle and sliders, the Triumph disc brake axle has a semi-circular cross-section indentation just in from each end of the axle; the outer studs on each disc brake slider are also apart only just far enough to fit in the indentations, the axle cannot slide laterally in either direction even if the slider axle caps come loose.

Thanks, Rudy. Great info!

Yes - my plan as of now is to use the Wilwood caliper and 2000 aluminum Sporty hub pictured earlier, which accepts the 11.5" rotor shown above bolted directly to its flange side (not shown in the image). Then, I'd put the tubes in the triple clamps (which have to come off anyway to R&R the headset, which is notchy and the bearings garbage, I'm sure), affix it to my tool stand/rolling workbench, and mock up the hub with disc between the '73 sliders currently en route.

From there, I'll determine whether I will need to dish the wheel slightly when I lace it up (and Buchannan can help me determine whether their off-the-shelf spoke kit for that hub has sufficient length for [x] dish offset), or if the caliper adapter design I've sketched will need [y] offset. I had said earlier that it'd be a single setup job on the big CNC mill, but it very well may need both sides machined to create the 'step' you see in my Spridget DIY rear disc brake adapters pictured earlier. Either way, of course, the bolt holes for the Wilwood caliper just need to move out radially ~1" plus a touch more from the existing position to accommodate an 11.5" rotor. So, we're talking a nice compact, very strong and good-looking adapter from 6061-T6. After all the years I've been selling the Spridget adapters to UK, Australian, and U.S. racers, not a single failure, and of course far less stress involved here...

Thanks for the clarification on the axle and centering. Hmmm... I may figure out a something similar here, but at any rate this is simple stuff and fun to do.

Okay, I'm getting excited about putting this hybrid front end together--oh, and I will buy or machine a brace. If I'm visualizing correctly, hard braking force would push the L/H stanchion forward a smidge, which I believe would be tantamount to applying negative steering so as to lean/turn the bike toward the left. In other words, pretty easy to detect whether that's an issue with some testing.

But for sure, one wouldn't want the bike to dart into oncoming traffic in a panic stop (on U.S. roads, that is--into the weeds on a UK road) on the two-lane blacktop leading up through the canyon to my place, which as you've seen is frequently awash in wild Mustangs (and then there are deer, per this recent photo from my driveway--the third buck is just out of the frame to the left), coyote, rabbits and rattlers...

The second pic is the Hyde brace you mention. Frankly, for $225, well worth avoiding the time and work to machine my own set, and not bad looking.

Question: do the adapter sleeves in the image tap into the disc brake sliders' seal recesses, and then the brace clamp onto those? I don't see installation instructions on his webpage vending the kit.

 

[Rudie]

View attachment 55963
do the adapter sleeves in the image tap into the disc brake sliders' seal recesses, and then the brace clamp onto those?

Regret I do not know, never used one. However, the original seals were about level with the tops of the sliders - the wiper protruded a little above - so I suspect the adapter sleeves fitted somewhere else on the sliders?

 

[NM Bonny]

Regret I do not know, never used one. However, the original seals were about level with the tops of the sliders - the wiper protruded a little above - so I suspect the adapter sleeves fitted somewhere else on the sliders?

Okay, thanks. I'll email them and see if they can send installation instructions as a PDF and post whatever they say.

 

[NM Bonny]

Hmmm... final thought for the night. Rather than turning down the ends of the Sportster axle to fit the '73 Bonny sliders, I may look into machining the passage for the axle in the sliders--and in the caps--to fit the fatter axle from the Sportster hub. Just a matter of whether there's sufficient material to safely do that.

But certainly throwing the axle in the lathe is quickest and cheapest route... either way, this will be one quick-stopping OIF Bonny.

 

[Rudie]

Rather than turning down the ends of the Sportster axle to fit the '73 Bonny sliders, I may look into machining the passage for the axle in the sliders--and in the caps--to fit the fatter axle from the Sportster hub. Just a matter of whether there's sufficient material to safely do that.

I found a new disc brake axle. It is 3/4" o.d., not the 5/8" I posted earlier - it must be the reduced diameter ends of the conical axle that are 5/8" o.d.? So apologies for the bum steer.

The distance between the outer pair of studs on each slider is 1/16" less than the ~3/4" between the inner pair, that the full diameter of the axle fits between. So the semi-circular indentation around the axle at each end, to fit between the reduced distance studs, is 1/32" deep, its centre is 3/8" from the corresponding end of the axle.

 

[NM Bonny]

I found a new disc brake axle. It is 3/4" o.d., not the 5/8" I posted earlier - it must be the reduced diameter ends of the conical axle that are 5/8" o.d.? So apologies for the bum steer.

The distance between the outer pair of studs on each slider is 1/16" less than the ~3/4" between the inner pair, that the full diameter of the axle fits between. So the semi-circular indentation around the axle at each end, to fit between the reduced distance studs, is 1/32" deep, its centre is 3/8" from the corresponding end of the axle.

Yes, I noticed that they are asymmetrical, re: the stud holes. My L/H cap was cracked, so I found some CNC-machined replacements for very little money on Ebay and they look well made. They look to be 6061-T6 temper, so the same material I'd have used were I making them myself.

Oh, no worries on the axle. A quick trip out to the shop reveals that the new bearings I had purchased for the conical hub are for a 3/4" axle, and the ends of the conical drum axle (which I can just measure where it protrudes from the clamps) are 5/8" as you had guessed.

So, it would appear that I might be able to use the Sporty axle to fit the '73 sliders to the Sporty hub. It just remains to measure the I.D. of the machined passage for the axle on the ends of the '73 sliders--and the spacing of the studs--to see if the new caps I bought for the conical drum sliders will work as-is or with a little machining. Hope so.

Here is a picture of the big CNC mill that is one of numerous machines in my next-door neighbor's shop (you'd never know he had a machine shop behind his residence nestled among the foothills, all run by solar power), and which will be used to churn out the adapter.

I could make a one-off part on the old dinosaur mill gathering cobwebs in the corner of the shop, which I recently learned how to use when machining an aluminum kick-starter for the '51 FL out of a tandem bicycle crank (the weight savings are hugely important to that monster's performance!). But if this conversion turns out well and I need to replicate the adapter for others who want one, that would make no sense.

 

[Rudie]

I.D. of the machined passage for the axle on the ends of the '73 sliders

The ends of the Triumph disc axle are 3/4" o.d., they were not turned down to 5/8" like the conical hub axle.

spacing of the studs--to see if the new caps I bought for the conical drum sliders will work as-is or with a little machining.

Regret to rain on your parade here but ... because the ends of the conical hub axle were turned down to 5/8" o.d., but BSA/Triumph still used the 1/32" deep indentation at each end of the axle to locate it laterally between each slider's outer pair of studs, all four conical hub slider studs are 1/8" closer together across the axle than disc slider studs ...

 

[NM Bonny]

The ends of the Triumph disc axle are 3/4" o.d., they were not turned down to 5/8" like the conical hub axle.


Regret to rain on your parade here but ... because the ends of the conical hub axle were turned down to 5/8" o.d., but BSA/Triumph still used the 1/32" deep indentation at each end of the axle to locate it laterally between each slider's outer pair of studs, all four conical hub slider studs are 1/8" closer together across the axle than disc slider studs ...

Sounds good - thank you.

Well, that just means I'll have to sell the conical drum caps I purchased, together with the OEM built wheel and sliders, to someone restoring a '71 OIF bike. So, someone will have a complete, copasetic set.

 

[sikatri]

Sounds good - thank you.

Well, that just means I'll have to sell the conical drum caps I purchased, together with the OEM built wheel and sliders, to someone restoring a '71 OIF bike. So, someone will have a complete, copasetic set.

An awesome alternative! Someone will be lucky!

 

[NM Bonny]

Everyone:

Another idea I hadn't seriously contemplated but which just jumped into my head looking at the bits in the garage would be bolting on the Sporty front end. The stanchions are 39mm, and the sliders proportionately fatter, so visually the front end would not be as sleek, but of course everything would be far stouter and the dampening feels very good, shoving down on them...

Obviously, there would be zero work involved re: the rotor and caliper, as the above Wilwood caliper is (I believe) a direct replacement for the lump of cast iron that comes on Harleys of that vintage (and which is fitted to the '51 FL DIY hybrid front end I built, seen earlier). Well, of course there'd be resolving bearing/race issues, and making up little fender mount adapters from 1/16" or 3/32" aluminum plate--no biggie. Unbelievably, the OEM '71 headlamp and its funky wire mount, and the '71 gauges with their pressed metal mounts, would bolt right onto the Sporty's aluminum triple clamps.

The Sporty front end--with axle and aluminum triple clamps but sans hub--is 27 lbs 13 oz. (The aluminum hub with bearings is 4 lbs 7 oz.) I am eager to to weigh the OEM '71 conical hub front end--with axle and iron triple clamps--to compare. That will happen fairly soon anyway, as I need to R&R the headset bearings and races, so I'll post the numbers.

Ultimately, I am far more likely to keep the front end looking (and being) mostly vintage Triumph components, save for the hub and brake as we've been discussing. But I'm curious to see how much heavier the sporty front end is. I'm guessing quite a bit...

 

[NM Bonny]

I found a thread discussing the Hyde 12" conversion and this link to a master/slave cylinder ratio chart. The latter is a useful resource I thought I'd share (I'm already familiar with that stuff through my R&D for the Spridget rear disc conversion; my DIY '51 FL disc conversion used regular Harley stuff so was a no-brainer.

At any rate, I'd rather roll my own...

That said, the adapter bracket in the attached photo of the Hyde conversion is helpful, as it mirrors what I had in mind to move the Wilwood caliper out for the 11.5" rotor.

 

[NM Bonny]

So, the sliders arrived, and three things:

First, they are clearly the later version Rudie mentioned, in that they have the groove machined into the top inner lip for the seal-retainer clip--same setup as with the late model Sporty sliders. Very cool.

Second, no way I'm putting the Sporty front end on this bike: these are 50% lighter than the Sporty sliders. I had expected a noticeable difference, but 50%? That's a lot of unsprung weight--and I definitely like the slender, elegant look of these vintage parts.

Third, I double-checked the eBay add, and it clearly states "New: A brand-new, unused, unopened, undamaged item..." However, they are self-evidently used--so not NOS--and show little scratches from installing/removing, grease and wear on the studs, wear in the bores, etc. (see pics)

Bottom line? I'll keep them but the eBay seller, who goes by "bsa***a70" insists despite the photos sent to him that they are NOS, refuses to issue a partial refund, and is clearly not to be trusted. Beware if purchasing an item from him: his descriptions may be false, as in this case--or as we ex-prosecutors call it "fraudulent."

Ah, well. I will have to sand and polish the exteriors, hone the bores, etc. A bummer, but it'll still be a pretty, functional, vintage upgraded front end when all is said and done.

 

[Rudie]

will have to
hone the bores

Imho, I would not bother; because the sliders are aluminium and are not bushed for the stanchions, ime those internal scratches will reappear shortly after using the forks again. Also the scratches are vertical, will not retain oil whereas honing marks would?

Btw:-

. BSA/Triumph recommended ATF for those forks; with the advent of proper fork oil, I have been using it for decades, Bel-Ray in my case; information posted in various forums suggest Bel-Ray 5- and 7.5-weights appear to a good viscosity match for ATF.

. Be aware, the ability of fork oil makers to match the viscosity of a container's contents with the labelled viscosity varies - there is a chart somewhere on the web that shows a large number of fork oil makers/products and the differences between a given container's contents and its labelling ... it showed Bel-Ray as close. However, depends what you can get easily - maker does not matter as such just, if you experiment with different viscosities, stick with the same maker?

eBay seller

Your experience is why I stopped using eBay years ago, unless it is a specific used part not currently made or I know the seller by external reputation. When buying from bricks-and-mortar sellers, UK consumers appear to have much better legal protection (including simply just changing your mind within a month after purchase) for a full refund than US consumers? Plus UK law places a joint responsibility on credit card companies - if I pay by credit card and the seller will not meet legal obligations, I simply call the credit card company and, worst case, they just take the money from the seller's account and repay me. In UK law, the lower limit on transactions is £100 but ime, a 'good' card holder, certainly some companies will battle with a seller even if a given transaction amount is lower.

 

[NM Bonny]

Imho, I would not bother; because the sliders are aluminium and are not bushed for the stanchions, ime those internal scratches will reappear shortly after using the forks again. Also the scratches are vertical, will not retain oil whereas honing marks would?

Btw:-

. BSA/Triumph recommended ATF for those forks; with the advent of proper fork oil, I have been using it for decades, Bel-Ray in my case; information posted in various forums suggest Bel-Ray 5- and 7.5-weights appear to a good viscosity match for ATF.

. Be aware, the ability of fork oil makers to match the viscosity of a container's contents with the labelled viscosity varies - there is a chart somewhere on the web that shows a large number of fork oil makers/products and the differences between a given container's contents and its labelling ... it showed Bel-Ray as close. However, depends what you can get easily - maker does not matter as such just, if you experiment with different viscosities, stick with the same maker?


Your experience is why I stopped using eBay years ago, unless it is a specific used part not currently made or I know the seller by external reputation. When buying from bricks-and-mortar sellers, UK consumers appear to have much better legal protection (including simply just changing your mind within a month after purchase) for a full refund than US consumers? Plus UK law places a joint responsibility on credit card companies - if I pay by credit card and the seller will not meet legal obligations, I simply call the credit card company and, worst case, they just take the money from the seller's account and repay me. In UK law, the lower limit on transactions is £100 but ime, a 'good' card holder, certainly some companies will battle with a seller even if a given transaction amount is lower.

Good point on the slider wear. I may ultimately machine the sliders for bushes; we'll see how much slop there is when I begin the mock-up assembly to design the caliper adapter--which will roughly resemble the part in the above photo of the Hyde conversion kit (not much room for innovation. as we're just moving two holes out radially and accommodating the Wilwood's span). I had to hone the used (chromed) sliders I got for the 'paint shaker,' but that was due to leftover chaff from the plating, and some considerable corrosion in the bores. The wear marks on these sliders are negligible in depth and there is no corrosion farther down inside, so they may well be fine.

I had forgotten the viscosity needed on these bikes was so light. The 'paint shaker' uses 20W but it is easily 100 lbs heavier than this bike (I can't push it up the apron into the garage, whereas the Bonny rolls in like an overweight bicycle). Thanks for this; I'll order some.

Yes, too bad about the eBay crook. It seems the UK has better consumer protection laws than the U.S., where business and property rights have trumped human rights since the git-go.

However, it appears these used parts are serviceable and new ones are 4x as expensive (I had written 2x earlier but got the math wrong), approaching what I paid for the bike! So, a Saturday spent sanding and polishing the exterior of the sliders on the buffer wheel the wife got me for Christmas, some new seals, and she'll look and handle fine. At least the dust scrapers I had bought for the conical drum sliders will fit these just fine...

On that front: thank you for taking the time to provide the part numbers. After some searching, I was able to locate the 'leak proof' seals, retaining washers, and snap rings. I have ordered the refined, fiber damper valve seals, too, for now. I may ultimately go for upgraded dampening mechanisms, but will be sinking a lot of bread into the rims and spokes, the Wilwood caliper, and per the chart I posted, an appropriate master cylinder to fit the 7/8" bar. And, I have yet to crack the primary case, so may discover a knackered clutch basket, etc. Need to preserve my dwindling funds to get her running!

 

[NM Bonny]

Now that I look at the proposed Wilwood caliper, which is made for pre-2000 Harleys, it's configured incorrectly to work analogous to the Hyde conversion (see 2nd pic), and a similarly designed adapter. What I need if I want to go the DIY route is a different Wilwood, shown in the 3rd pic. 3.55" bolt spread but same radial orientation as the caliper used in the Hyde conversion.

The Hyde conversion is $586 plus shipping, but assumes a Triumph hub I don't have. The properly configured, 4-pot aluminum Wilwood caliper is $247 on Summit Racing, the hub and rotor I've already got, and then there's just an axle and adapter I'd need to make.

Easiest would be to get another 3/4" 'wide glide' axle such as I used on the DIY for $50, then if things work out, just part it off in the lathe at the appropriate length. Both the axle and caliper are returnable within 90 days, so can be used for the mock-up exercise.

So, the plan is:
1) get the 3/4" Triumph clamps in (on the way)
2) get an axle;
3) get a caliper; and
4) perform the mock-up to confirm 'proof of concept' on the adapter design.

The rest is a breeze--and if it doesn't work, I can always punt to the Hyde conversion...

 

[NM Bonny]

Gentlemen:

I couldn't stand the suspense, so after scratching me heed for awhile, figured out a way to take 'go-no go' measurements for this proposed DIY conversion re: the hub--but someone check my logic and math, please, as I'm tired:

1) The 2000 Sporty hub pictured earlier is 4.75" wide with the disc fitted (it sits flush on a circular centering step machined into the hub's L/H side).

2) There is a little raised, semicircular flange surrounding the axle that is cast into the Triumph sliders' inboard surfaces, and measuring from that surface outward to the center of each slider (easy to locate with the whole drilled in the bottom) is conservatively .9335", same on both sliders.

3) I believe the stanchion centers are 6-3/4" on the OIF models. That looks about right using the decidedly inexact method of holding a tape up to the chrome caps on my '71 Bonny, albeit with the handlebar kind of in the way. Rudy: are the stanchion centers 6-7/8" or 6-3/4" on these OIF bikes?

At any rate, assuming Rudy (or someone) confirms that it's 6-3/4" centers on OIF triple clamps, we have:
6.75" - 1.867" = 4.883" clearance between the sliders' semicircular, inboard axle flanges
4.883" - 4.75" hub = .133" clearance, or just over .125" which is 1/8"

This math, if correct, yields three kinds of good news:

First, I won't need to dish the aluminum wheel when building it. Simply buy Buchannan's off-the-shelf stainless Sporty spoke kit and lace it up centered to the Boranni drop-center aluminum rim.

Second, it's easy-peasy to machine or just buy 3/4" I.D. shims in stainless to center the hub or shift it ever-so-slightly away from the L/H slider if the disc is too close for comfort.

Third, it would appear from Solomon's earlier photo that the stock rotor runs bloody close to the slider--as does the Sporty's, by the way. This means that the caliper adapter design should be very straightforward indeed, for as we saw in the Wilwood diagram in the last post, the mount offset is .70" to the center of the rotor's cross section (the 11.5" stainless rotor I've shown earlier is the correct diameter and .20" thickness for this caliper).

And now, I can sleep...

 

[Rudie]

believe the stanchion centers are 6-3/4" on the OIF models.

Correct.

stock rotor runs bloody close to the slider

Correct ...