The 73 was the first year for BBP with disc brakes, with drums you still had SBP till 76 I believe. So I would say the 73-76 drum brake setup still used the small upper ball joint.
The 1973-1976 drum front brakes remained SBP, but the spindles and drums changed over in November (ish) 1972 (73 model year production started August 72). From that point on all the A bodies used large upper ball joints. Disk brake cars were large ball joint and big bolt pattern, drum front brake cars were large ball joint but remained small bolt pattern until front drums went away entirely.