Just checked on the rear calipers for a 75 I've got in the garage. It looks like they are a 2 piece casing that is bolted together.
I know the SZ/RZ has vented rear disks, but the question is, are SZ rear calipers the same as the 75, apart from a spacer between the 2 halves to increase the gap to allow for the thicker vented disk?
Land Rover do this to allow basically the same caliper to be used with vented/solid disks.