72 Plymouth Duster Backspacing

Large or small bolt pattern?

If it’s an A body 8 3/4 with the stock SBP axles then 4” is usually a better backspace. With BBP axles and a 15x8 with 4.5” of backspace you should be fine. 3.5” of backspace only works if the car is sitting fairly high in the back, at stock ride height that usually put the tires into the quarters.

And there’s always the wildcard, the axle could have been shortened.