During the performance wars, the battle was just as big, if not bigger, within the GM divisions. So I doubt that any head brass of any division would have allowed one of its cars to leave the plant powered by other than the division's engines. Maybe divisons may have done so, and maybe after the performance wars, but during the performance wars, I doubt that John Poncho Deloran would have allowed one of his cars to roll out of one of his plants with other than Pontiac engine. That would have been about the same as chevy or ford sending out cars with the other's engines.