I'm trying to install a NOS set of XT-2 cantilever brakes on my bike. It's a Trek hybrid that I've had Avid Shorty 6 brakes on for a while without an issue. The problem that I'm having is that the part of the caliper that slides over the frame boss is significantly shorter on the XTs than it is on the Avids. It's so short, in fact, that the boss protrudes out beyond the caliper when the brake is fully seated on the boss. It's preventing the mounting bolt from seating on the caliper, so the brake is free to move all over the place.
In the first pic, the brass bushing is the innermost part of the caliper, and the steel boss can be seen sticking out just inside of it. Same exact thing happens on the old Schwinn hardtail I tried it on. Any idea what's up here, or what I can do about it?