Keep in mind the BBP swap with aftermarket Axles and BBP drum widen the track. I believe the consensus is ~3/8" per side, 3/4" overall. On the 67-69 dart this makes wheel choices difficult when you get into wider that 6" rims. You'll need more positive offset (Larger backspacing) with wider rims. Ideally a 7" wide rim would have a minimum of -6mm to -12mm offset to fit without rub a dub dub with the proper tire. Match the tire to the wheel width. 215 to 235 seem to be a good width to run all the way around if you want to rotate.
I'm a advocate of 17" wheels. Tire compounds, sizes, selection and availability are far far greater than 15" and typically the same or equal too in price for a far better tire.