You could not buy a 396 "new" in the 80's if they were to use or swap anything it would have been a 454.
I know you couldn't. If you read my full post I said they may of had extra 396's laying around in case the older Elkies blew a motor. Would a fresh 1969 motor still run in 1982 if it had never been used? I've read many articles stating the G-bodies had 396's in them.