Rim size and backspace, housing lenght for minitubs?

Minitubbed `71 Duster, will move the springs inboard to the rails. Looking for widest wheels that still have decent tire clearance - 15-8.5" or 10"? Also need to figure out width for rear housing that will let me use standard offset/backspace wheels as I will be most likely buying them used so I don`t want to be hunting for a specific backspace or having to order new. I checked the wheel tire combo thread but not enough info for minitubbed cars.