In 1973 when the A body cars were first available with the large bolt pattern and front disc brakes, the upper control arm was redesigned and used the larger ball joints shared with the B and E body cars. The cars with 10 inch front drums also used the redesigned upper control arm. There WERE also a few cars built with 9 inch drum brakes that still used the same upper A arm as in all previous years. This arm used the small ball joint and will not work with a 73 and later disc knuckle. I have read of a few companies that are reproducing the upper control arms. I seem to recall Magnum Force racing? Not quite sure. CAP products makes new lower arms.
The B and E lowers used a different pivot shaft with a larger diameter and a "step" that keeps them from being a direct fit. I'd guess that if you changed out the pivot shafts, they would fit, but they are also supposed to be shorter from the pivot shaft to lower ball joint, so this would certainly make aligning the car an interesting situation....
