I spent yesterday following @Eric_Shea 's how-to instructions on his website and youtube to disassemble my brake calipers to prepare for sending for plating. My car has one early and one late rear caliper that I don't think has anything to do with my problem but just another of many examples of the mismash of early/late parts on my mid-MY 73.
Three and a half of the calipers came apart without a hitch, which is amazing considering this car spent 30 years outside with brake lines opened up. All pistons came out without an unreasonable fight and no fasteners were seized. The problem is with removing the last (inner) piston on that early rear caliper. Spinning the adjuster doesn't move the piston. It feels like the gear is engaged but turn and turn and nothing happens. Cranking the e-brake lever moves the piston out about 3mm and then it goes back when the lever is released. There is no ratcheting of the piston position. I have NOT split the halves of this caliper yet because it is the only one with Ribe fasteners and I'm waiting for my Ribe bit to arrive in the mail. Since the caliper is still together, I tried popping the piston out with compressed air but that does the same as cranking the lever - piston moves out about 3mm and then goes back. I'm not sure what to try next. The only thing I can think is to go ahead and split the caliper and try gently tapping the piston with a wood drift to try to spin it off the adjuster screw. Anyone have a better suggestion?