1970 Ebody 2 piece rotors

Does anyone replace the rotor part? Can they be rebuilt? Thanks.

1 piece replacement rotors have been available aftermarket for many years. I assume they are still available.
As far as original 2 piece ones go, they haven't been available new for decades, other than lucking into or paying through the nose for NOS ones.
Original used ones can be cut on a rotor lathe if there is still enough material available to still have the minimum allowable rotor thickness left after cutting. That's about the only way to "rebuild" originals.

The new one piece rotors are better, and stronger than the two piece ones.