I had one that the slide pin was so rusted up that it took me 2 hours in a fully equipped shop the night before a ride, to get it apart and back together. There is a thin wall bushing in the caliper. The pin is supposed to slide in that bushing. When I finally got the pin pressed out, the bushing was stuck to the pin. I made special press fixtures in the lathe, drilled the center out of the pin in the drill press, and pressed things apart and pressed the bushing back into the caliper in the hydraulic press. In desperation, I used a front caliper slide pin. It works, but there's no way to seal out water. If you use a complete front caliper, you still need the rear caliper mounting plate.
Here's a thread that shows a right front caliper on the rear.
http://bansheehq.com/forums/index.php?showtopic=152261