Gary,
What I know, which may be subject to revision, you can do 3 or 4 things. Replace the original parts, gotten from OB for about $90. But you have to do the shim thing and figure that out.
Other thing to do is the Norvil conversion, I don't think it requires any changing of your current setup. Grandpaul also sells the same outfit, I think. At least that's what I gleaned. I think it has vernier adjustments, so no shims are required, but it is a different setup than original.
Another option, OB parts for $90, and the Hemmings vernier adjusters, I think they are about $150, but I haven't checked the price lately. They just replace the outer bushings on your current setup. That's what I'm going to do sometime.
So it sounds like the only advantage it the MK3 iso's is the vernier adjustment. The same advantage applies in adding any of the other vernier style adjusters. It appears dialing in the isos can be a tricky process. I would like to hear both arguments in favor and against the vernier adjusters.
There has been some discussion about early 750 and later 750 and 850 rubber bushes. You don't want the later rubbers, because they are too stiff and will give you more vibration. I'm really unclear on this though. I replaced my bushes with the OB ones, original part numbers and it seems to have more vibration than I remember, but I was riding with really old bushes, and the exhaust parts were banging on the iso nuts. It does seem to be getting better as I put miles on the bike. Some people have even drilled holes in the bushes to make them softer. I had a discussion via emal with Phil at Fair Spares and he sells the original soft bushes. I almost wish I had done that than the OB ones, but I don't have anything to compare so I can't really say what the deal is.
How many of you 750 owners would like to testify about the use of 750 iso's over the 850?
That's been my experience, good luck. What ever you do, I'd like to hear how it works out.
Dave
69S