'69-72 single piston setup is good option. The '73 spindle is a unit set up for larger bearings so the '69-'72 rotors do not fit that spindle. The '73 spindle shares the same rotor as the 1/2 ton van and pickup and those parts are still readily available. The '73 is the best choice. Calipers are the same for '69-73. You will also need a Bendix dual diaphragm booster to power the disc brakes and a brake proportioning valve and the required tubing to hook it up and balance the brake system.
