1) Most likely talking about an aftermarket over the counter part(s). M21 most likely not original to your car as it was not offered with a 350-300hp.
2) He was having a delusional thought from a failed memory. No such thing.
3) ONLY manual Sm. Blocks have smog in 69. If it has a provision for smog tubes, it should have smog. If not, the manifolds are either replaced or the car was originally an auto trans car.
4)Not much can be said or done about that. Need to see a pic to verify.
5)Yes, I have seen painted (different than factory) Ralleys. Steel wheels were not an option, they were what you got if you did not check off an optional wheel like a ralley.
All this info is useless without a picture collection of relevant items, like the trim tag, dash, wheels, POP, Trans code etc..Right now, it is just speculation. How many owners between you and original owner? Any # of owners could have switched/painted parts etc.. and do not rely on geezers (like him or me) to have a faultless memory. Us old guys have been known to embellish things too. Another thing, just 'cause (I assume Father's name) his name is on POP, does not mean he was the original owner, it could have been sold under warranty and a new POP issued with some alterations done prior to his ownership. And 2 brothers shared car? No telling what was changed or done that each would have a different recollection or story. Good luck, welcome to the site and let us learn more about you, your car and how you came about owning it. Thanks.
