They probably used the 73-76 A body spindles with pin style caliper brackets.. They bolt together with zero modification and you get a better caliper mount..
Yeah with the way they sectioned the UCA I bet the whole thing was from B/E body donor, spindles included.
So I’d definitely check the wheel bearing size before I started ordering parts. Nothing wrong with the 70-72 B/E body spindles but the wheel bearings and rotors are different than 73+.