I guess I'm still obsessed with brakes. Re the elusive early Dura-Ace centerpull calipers, would their design and looks be similar to Shimano 500 cpulls? I have a pair of these...their most distinguishing feature is that the brake cable attachment is asymmetric as a cradle (saddle) is attached to one arm directly and I think a straddle cable would then connect to the other side. This cradle (or saddle) also is part of the QR mechanism. Sorry if my description is vague as these 500 calipers are missing a bit or two.
Jack Romans
Sacramento, CA