Disc brake master cyl bore size.

Looks like the 1973+ front disk kit, including spindles. But, they somehow got the integral hub-rotor made w/ studs on a 5 x 4"D bolt circle. The standard rotor from a parts store would be 5 x 4.5"D bolt circle. My guess is they custom-ordered from the factory that way, or somehow bought the rotors undrilled and drilled their own stud holes. I don't know if the center register hole for the wheels is bigger in 1973+ cars. If so, they probably did even more customization.