i have a '75 and I was able to get a 28x10.5 MT ET drag under it on a 15x8. I had a b body 8 3/4 so I had 5.5 for backspacing.

'75 Plymouth Duster
Phase I 451 906/590/2-660 10.75/126
Phase II 451 Stage VI/590/1050 9.82/135
Phase III 383 906/Victor-Pump gas 11.30/119

"For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,"