I noticed a difference between Weinmann center pulls and Dia Compe calipers that look identical. The Weinmanns have two windings (or really one and a half) on the springs, and Dia Compe have three (or really two and a half). You can see this from the sides or tops.
Another difference I noticed was in performance. On bikes equipped with Dia Compe brakes, the leverage was higher. You needed less hand pressure, but if the brake wasn't adjusted tight, the lever would reach the bar before applying full force. We used to say that they felt spongier. I think the difference was in the lever, not the caliper. Perhaps the pivot point in the lever was closer to the cable attachment point in the handle. I don't know for sure.
Dia Compe:
Weinmann:
