what size wheel for 72 Dart?

Great info so far, the part that is missing is the rear axle. It makes a difference if you have an 8 3/4 or 7 1/4 rear axle, and it makes a difference in the backspacing if you have the factory SBP (5x4") or BBP (5x4.5").

With an 8 3/4 and BBP axles to run 255/60/15's I'd be looking for a 15x7 with about 4.75" up to about 5" of backspace, closer to 5" if you've got rear disks or plan to add them.

If I recall correctly, @toolmanmike has 15x7's with 4.25" of backspace, and a SBP 8 3/4? And maybe closer to 4.5" would be better?