Hey
1989Pre gimme a sec, let me blow your mind. DON'T BUY ANYTHING.
I just popped off one of the pivot bolts from a crappy old pair of MAFAC Racers. Guess what? IT'S THE SAME BOLT!
Pop one of yours off and see if it fits. If it does and you don't have a spare, PM me with an address. Will only cost me a buck to get one out to you. I have MAFAC stuff coming out my ears. Won't be the prettiest but it'll clean up.
The only thing that bothers me is the absence of the 'nub' on your adapter which I think acts as a pivot bushing of sorts for the caliper. You could probably find a ferrule or bushing to mimic that, though.
