I know of a couple 62 Bel Air four door cars that came from the factory with a 409. No reason they couldn't, check the serial number stamp on the passenger side of the engine and see if it matches.
Yes, I saw a 1963 Biscayne 4 door at the old Pate Swap Meet in Cresson Texas about 15 years ago. The car was out of San Antonio, Tx and was a faded blue. It was a 340 HP. automatic trans.
I miss the old Pate swap meet. Nothing like a little cow crap on the bottom of your shoe while looking at rusty gold. Sorry a little off subject just brought back good memories! Back then you could order just about anything. I would not doubt it could be real.
Years ago there was a black 4-door...either Belair or Biscayne..........that was totally original and frame-offed...425HP 4-speed. ULTIMATE GROCERY GETTER!!!!