Exactly. And a '72 is no different for rear tire clearance than a '74, or a '70, or a '76. All of the '70-76 Duster/Demon/Dart Sport cars all have the same rear tubs and quarter spacing. The backspace changes because the rear ends used were different widths from the 8 3/4 to the 7.25 and 8.25" rear axles, and BBP vs SBP etc. But the spring to quarter distance should be pretty much the same, allowing for factory body tolerances of course. It's definitely tight, and on a car that ended up on the small side of the body tolerance it might not work with a given ride height, but the majority of those cars should be able to run a 275/60/15 if the backspace is correct for the car.