The caliper they're using in the above thread is from the '86 to '91 2nd gen 5 lug turbo or NA Mazda RX7. It's a 4 piston non-staggered bore cast aluminum caliper designed to run with a 276 x 22mm rotor and 15" wheels. So it combined with the 287 x 22mm 740/760/940/960 rotor there is only a 5.5mm radius difference. This is definitely the route I'm going since all the parts are so cheap and will fit inside my new wheels. All I need to do now is fab up an aluminum adapter bracket to hang the caliper.
