1971 Demon Brake Question

Mopar 10.7" Rear Disc Brake Kit

Those are your best bet, I have the bigger rotor version and they work well and get the parking brake cables too. It all works great. It's a 94-04 Ford Mustang Cobra brake caliper.

Most of the other kits that are cheaper use those really old Eldorado calipers (pins are exposed) and those calipers are just hot garbage.