i know a little bit, so heres most of it.
the old sonny routt kit was from the 1960s. routt is a famous hot rodder from the 50s and 60s who was contracted in 1969 to make 750 kits for the factory racers, since he was already doing them on his own. the modern routt kit is made by aerco, i think. on the outside it looks just like the 650 barrels. keeps the tappet oil feed and comes stock at 744cc with 8.9 to 1 pistons.
the morgo kit is the only one ive personal experience with. 740cc at 9.5 to 1. the fins are extended out to match the head and the tappet oil feed is deleted, which requires you to use a later exhaust cam, which you probably ought to be doing anyway.
i think both will take standard valve sizes, but if you go bigger on the morgo you will need to open up the valve pockets on the pistons, which is easy to do. both kits are bolt-on, and can be fitted to pre-units if you use a 9-bolt cylinder head. you dont need to re-balance the crank unless your butt is more sensitive than mine.
since the original stock 750cc jugs were set at 8.6 to 1 you would want to pay attention to detonation, especially with the morgo. fitting an EI with a slower rate of advance might be all you need, else you can mess with fitting the pistons super close to the head to increase squish using different base gaskets or maybe cutting the head down some, which causes pushrod tube issues for you to solve.
i just have my cylinder heads drilled for two more spark plugs, and that solves all the detonation problems forever. cheap and easy.