Disk brakes 1977 volare into 1968 barracuda

That Mancini rotor says 62--72 A body in the description. Also says NOT a replacement for the factory KH rotor. So it bolts to factory disc spindles up to 72 and uses a later caliper. Kind of an orphan, it will not work with the later spindles. IIRC, the bearings for the 73 and up spindles are all the same.

It will not work for what you're doing. If you want discs and keep the small 4" pattern, finding a factory KH setup would be best.