Balilla center pull brakes have this nice builtin drop bolt feature. Instead of round holes in the backing plates (stirrups), they have slots which allow you to move the entire caliper up or down by rotating the bolt 180°. I have a pair of these I'd like to use on the back of my Dawes as the drop bolt feature allows me to lower the caliper for 700c rims. Unfortunately, both bolts I have are too short, even for use on the rear:
That short bolt barely makes it through the backing plate and the brake bridge with a semicircular aluminum washer to mate the flat backing plate to the round brake bridge. There's not enough room for a washer and nut on the back (front) side (let alone the matching semicircular washer). My guess is that the bolt shown above was for use on a low-end bike with a flat sheet metal brake bridge.
I need something longer, probably 35mm at minimum, 40mm to be on the safe side. I tried swapping in a center bolt from a MAFAC Racer, but its diameter was too large to fit through the slightly narrower slot on the Balilla. (If it would have fit I'd have cobbled something together to take up the extra space in the slot.) Anybody got something like this? I'd be happy to buy an entire caliper (or set). Happy to trade as well. I have plenty of small parts to trade. If you need something, let me know.