What caliper is this

It's a slider type caliper. The piston diameters on the calipers used for the 11 3/4" and 10.95" rotors are usually the same (at least for a few of the years). But, the pistons for the 73-76 A-body calipers were smaller. So there are at least two different sized pistons. Might be more. But regardless of the piston diameters all of those calipers fit all of the brackets, so you can run the larger piston calipers on a-body 10.95" brackets, or A-body calipers with the slightly smaller pistons on 11.75 brackets. As long as they're all slider brackets and calipers.

The piston size isn't a huge difference, but you can get a little more braking power with the non-A body calipers.