71 Dart Swinger wheel/tire combo suggestions

I wouldn't plan on going wider than 245/60/15 in the back. Some cars can manage a 255, but most can't. With a SBP 8 3/4 you might be able to get away with a 15x7" and 4" backspace, but really you should have more like 4.25" of backspace to fit a 245 even with the SBP.

In the front a 225/60/15 would be about the most you would want to run, especially with a 15x7 and a 4" backspace. That would be a no-go with BBP brakes, but with the SBP it would be about the max.

If you could find SBP 15x7's with 4.25" of backspace you'd be in better shape.