If it's a single piston caliper then it's the later 73+ disks and it's 5x4.5". There was not a lot of "mismatching of parts", and regardless all the factory single piston calipers were part of the BBP disk set up.
In 1973 the disk brakes changed from the SBP Kelsey Hayes disks to the single piston BBP disks. The upper control arms also changed to accommodate the larger ball joints that were used. Basically the A-body cars went to using the same brakes and ball joints as the other model lines. The 1973+ V8 cars came with disk brakes standard, so they were all BBP. The slant-6 cars still came with 4 wheel drums standard, and the 4 wheel drum cars were still SBP (but got the larger ball joint UCA's still). But, disk brakes were an option on the slant 6 cars, and if they got disks they were BBP. And some of the other options triggered the disk brake option too, like a towing package, so quite a few /6 cars ended up with disk brakes and the 5x4.5" pattern.
