what calipers do I need????

You have 73-76 A body disc brakes.
So, order up rotors for any 73-76 A body car.
Rotors are a one piece design.
Buy calipers for a 76 A body car, as they use a 2.750 diameter piston, as the 73, 74, 75, cars use a piston of 2.600 diameter. Slightly smaller.
Brake hoses for any A body car.
And i guess new control arm bushings, and ball joints for those upper control arms, while you have everything on the work bench.