I assume you are talking about non hemi disc?
People have been using the Raybestos MK551 kit to get the seals to rebuild those, kits with the correct primary piston haven’t been available for decades. However sadly that kit was discontinued recently.
I posted about this around a month ago on another forum-
https://forum.e-bodies.org/wheels-t...171-master-cylinders-discontinued/10767/
I’m not sure where if any correct seals ard available now that kit is gone. Maybe some kits are still out there at part stores somewhere, so grab any you can find.
A member here was selling kits he’d made up, maybe he still has them, I think it was NS1AAR.