Be careful about buying replacement pistons for stock rear Girlings. The floating piston with the metric threaded square-stud for e-brake adjustment is fairly simple to replace, but the other piston with the built-in clevis is a mess to disassemble/reassemble. I tried it and after getting three layers down in snap-ring retainers & broken plastic pieces, I carefully reassembled what I had and put it on a shelf 25 years ago. I suggest finding a good used caliper complete and working with that. Larry Stock at PPC-Carson City and (I think) Wilkinson in CA) both offer rebuilt stock assemblies, with your rebuildable cores.
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