The reason I am asking is because I've seen 1970-72 Grandprix with the Pontiac 455 engine without a 12 bolt rearend and some with it, I ask the American guys on the PY forum and they say all 1970-72 GTO-Lemans-GP's 455 powered cars came with the 12 bolt rearend, I guess here in Canada they installed whatever was available 10 or 12 bolt.
No, John Delorean would not permit it. Remember the GP was his baby, the executive muscle car. I was lucky enough to drive a 1973 SJ that belonged to my wife's aunt and man that was one fast car, can't imagine the earlier ones. Had a 1980 and a 1989 but goes without saying, no comparison.