15x7 is standard cop wheel (with 4.25 BS) and fits wonderfully, but you can't go much wider than 215 depending on ride height and aspect ratio.
but then the issue is that with the smaller diameter rim you can't get much more backspace because you'll get into the tie rod or upper control arm/ball joint.
when you add in the 73~76 spindle that increases track width things become even tighter, especially with the darts, vals and narrow body cars.