What would the PHS say?
That it never was built with a 455 from the factory would be my guess.......
OR.....That it was an extra 76 455 car converted to a 77 for the movie, SATB???
Supposedly none of those cars survived is the long standing story though.
Sending a 76 engine out to the public in a 77 body would leave Pontiac open to the EPA. I doubt they would expose the company to a fine and penalties just to make some dealers kid a special car. Especially when they would have to stamp the 77 VIN on a 76 engine to make it all legit.
Usually when someone starts telling me one of these tall tales, I just smile, and nod, then walk away.......