I have found aluminum drums on gbodys, box caprices and 3rd gen fbodys in the wrecking yards. I think you can also find aluminum bumpers on other gbodys. My 1980 monte has them
All 86 regals including ttypes and gns got al bumper spports. The 87's got the heavier steel.
All non posi turbo regals got the Al brake drums.
But the real gnx wheels were $4,000 for a used set 10 years ago, while gta front wheels are $900 for a brand new set. It would take a hardcore cloner to put a set of real gnx wheels on a clone car and if a real gnx for sale with gta"s on it (and no GNX wheels), I take $8k off my offer.