I started there first. Their "read this first" post suggested that for older stuff (this is on a 90s mtb) c&v might be a better place to ask, so I tried here first. I think I managed to get it back together. I broke down and pulled one of the back arms. I really hesitate doing that, since I fear I can wind up with two sets of disassembled brakes and no reference. Still would like suggestions about the manufacturer and model of these brakes, so I can track down some diagrams.

Eh... Diagrams might not be available. I spent some time looking for the bike. It's a Schwinn Sidewinder. Looks to be a 1996 model (thank you Waterford for the catalog scans). If correct, it has Chang Star cantis. Not likely to find an exploded diagram for them.