1972 Plymouth Scamp

The '72 production year began in early August of '71 and went to July of '72.
Your car is a mid November built car, so it's scheduled build date is roughly in the first 1/3 of the production year.
So, it's a given that big bolt pattern stuff wasn't available for the '72 model year A-Bodies let alone 8 1/4 rear ends, we can deduce that it was installed at a later date and wasn't factory original to your car.
If the car has the original driver's door on it, there should be a grey and black sticker on the door itself by where the door latches to the door jamb striker that has the V.I.N. on it and the month and year of production, G.V.W. etc...........
Does it have any of this info?
Just trying to help you with the sale............