You just need the spindles for a large-pattern swap. All the A-body upper control arms changed to the big ball joint in '73, so they're not disc-specific. '73-'74 E-bodies use the same upper control arms, for the record.
On the flip side, if you wanted to use the '65-'72 Kelsey Hayes 4-piston disc brakes, you'd need '72-older upper control arms, but again--they're not specific to disc brakes.