Widest rim in an A?

What is the widest rim/tire combo that could be tucked in the rear wheelwell of a 70 Dart Swinger that has been minitubbed and the springs moved inboard? Will also be using a Caltrac package with monoleaf. I will need as much tire as I can fit.

not talking about a strict drag slick either.Something street "legal" so I can drive it on the weekends.

What backspacing,rim width and tire width will I need?

thanks guys!
Paul