Re: 929, 954 front brake master cylinder piston size.
I just checked Ron Ayers and they have different part numbers for the calipers (seals, pistons, etc) but they are on the same microfiche page. I don't know about the caliper piston size differences but I will try to measure mine (1 929 caliper, 1 954 caliper) over the next week or so (I need to pull the wheels off the bike anyway).
FYI, I didn't order enough seals when I rebuilt my calipers so I could only do 1 of them. I had to do some side work for a salvage yard and picked up a 954 caliper for the 929 so I would have a complete set of good calipers that didn't stick. It bolts right on and I had good braking power during my races. If they are different sizes then I don't know that you will notice much, however, if you can wait though this week then I will attempt to measure both the 954 and the 929 caliper pistons for comparison.