[TimG]

An X code car would no doubt be a true Pace Car as no Cutlass Supreme hardtops other than a Pace Car can have an X code engine. A U 455 could be purchased in any Cutlass hardtop. As I understand, there was no way to tell a true Pace Car from the trim tag or ID number unless an X code.
I'm looking at a 1972 X code Pace Car for sale locally.
If it has the original spare it is a rare, rare Goodyear Polysteel 60 series made only for this car. Make sure it is not a standard Cutlass Supreme in white with a 455 dressed up like a Pace Car. They can also have an open rear end, no posi.