Old pistons were munted.
New pistons and seal kits, thank you Ebay.
Calipers are the same, but appears one is an earlier or later version, which ties in with the differences in pistons (could be from one of many cars, I believe they were used on Fords as well as BMC cars),
New stuff installed.
Hooked it all back up, bled the brakes and took it for a test drive. Brakes seem to work nicely _b
Edit: hmmm I think the head gasket might have blown recently, the fun never ends lol.