M50 15" tires on a stock duster.

I was hoping to get some information.My brother back and the seventies had a plymouth duster that had m50 15 on the rear. He said that they stuck out a little bit and you could stand on top of the tire and wash the roof of the car l o l. But he cannot remember the back space On the crager wheels. He did have air shocks or shackles.That kept the back end up. But he did not have any other modifications done Do the springs or their location Anyone have an idea on what Back spacing and size of rim he might have used