Some previous owner had either swapped the axles or the whole rear end on the car to get the 5 on 4.5in bolt pattern out back. The fronts however were still the small bolt pattern 5 on 4in kelsey hayes discs. Because 700 usd willwoods are not in my budget I decided to do this mod: Using mustang rotors for 4.5" bc
It involves reducing the outer diameter, lowering the bearing seat and removing the seal area on some 1965 mustang discs. Kelsey hayes made brake kits for fords too just with some slightly different specifications.
I managed to find a guy in my town who took care of them and made centric adapter spacers for the wheels from some fiber-derlin like material. He opted to CNC the bearing race as he was not confident that turning this part would be precise enough. Somehow he only wanted equivalent to 110 dollars for this so I gave him 130 because he was being almost too kind!
The discs really have shrunk for me, Im used to only seeing them on 14in wheels.