4 wheel disc troubles
They are definitely A or F body calipers
Don't forget- not all A body calipers are created equal- '73-'75 calipers used a 2.6" piston, '76 A body and F/M/J used a 2.75" piston.
From the factory, '73-'75 As used a .937 master cylinder for power brakes, and a 1.032 for manual.
1.032 MCs are listed for both power and manual brakes for the '76 and up calipers.
Additionally, the early power brakes used a 9.88 dia. booster, '76 and later got a 11.43 diameter diaphragm.
All the little differences can add up. As MoparLeo stated above, stick with the matched factory parts.
Adding rear discs complicates it a bit, but removing your rear residual valve was the right move. At this point, I'm thinking there's still air in the system- it can be real stubborn. You do have your calipers on the correct sides, with the bleeders facing "up", right?
