The hub is the same, but I agree with Randy, I think the caliper mounting bracket is different.
Also, those early calipers are more or less infinitely rebuildable. Everything that wears is replaceable. TRF will sell you rebuilt early calipers (likely Moss will too but I didn't check).
Yet another thing to check is the diameter of the mounting holes in your new calipers. I forget the change point offhand, but the holes got bigger at some point in TR6 production. Since it is important that the bolts fit snugly in the holes, there were $pecial bolt$ with oversize shanks to use with the later calipers.