I'll start with something you probably are aware of, each Triumph is uniquely it's own kettle of fish. Having said that, I may be in a position to guess as well as anybody what you are in for. A few years ago I came into possession of a similarly low mileage 1969 Triumph 500. It had broken (primary gear) and been parked over 20 years previous. It had been parked in a garage. There's quite a bit of info on the process on triumphrat 1969 T100R rehab thread . Mine seemed to have been through more than that one you are looking at. It was filthy for one thing. The front fender is gone. Aftermarket silencers. Dent in the fuel tank. And yet, much of it was unworn.
I will attempt a list of all the bits and bobs that have been replaced or renewed in the interim. Bear in mind, my thought process in the beginning was to keep it all original. Hah!
In no particular order:
All the fluids changed, anything that can be greased with new grease, greased
Air filters
Forks rebuilt as gators were in several pieces and seals were leaking. Additionally, I'm on my second set of new gators as the first lasted less than a year. IIRC, I got "10 year" gators from CBS the second go around and those are substantially better.
Steering head bearing
Carbs rebuilt including new floats and needles. Bike fuel had not been drained before parking. Tank and petcocks have not been a problem.
Fuel lines replaced.
Tachometer and speedometer locked up and needed repair. Speedo went first and took out the cable. The cable/instrument place in Canada is fantastic. I have cables from them and and their turnaround time on repairing the meters is excellent.
Vintage british cables
Plug wires replaced
Coils (siba) failed about 2 years in.
Tires and tubes (originals looked so nice except for the cracking sidewalls)
Chain
Pushrod tube seals et al (this was quite the engineering project-seek out Rudies posts on this as they were the clarification I needed to understand I was going to have to sort out the pads in a custom way) The seals sealed for almost 2 years, but when they stopped, it was quite the oil mess. The rubber down there was rock hard. It was disappointing at the time to have to tear down the engine that much after it was working just fine, but C'est la Triumph vie.
Battery strap
Kickstart and shifter rubber
Rocker box o-ring (this was a nice reminder that I did this, at the time I was not convinced the o-ring made it substantially intact to where it would adequately seal, but it is not leaking yet)
Gas tank rear mounting rubber
Shock mount rubber (actually only one fell to bits, the others seem fine)
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I think that's about it up to now.
My thoughts on value are this. I have always thought my bike was worth 4-5K. I kind of thought that before and after the work has been done. I can see how a person selling THAT bike would think it's worth more. However, they probably don't appreciate the amount of work it will require BECAUSE it has low miles. If you tally up my list cost plus labor, I bet you could illustrate how much less than 7k it is worth. I could easily see 7k after it's sorted. Kinda depends on whether a person wants to look at it or ride it.
Hth,
Daryl