Ford rotor(black) is 3/8" shorter than the Chev rotor. The Wilwood agent recommended 0.482 caliper spacer which is almost half inch. Other spacers are 0.357" and 0.407" would be closer to 3/8 difference. I didn't want to have to go back and forth trying to get it just right but they also have a couple shims and spacers on the bolt kit.