The 15x7 wheels from a Chrysler 5th ave, 86-89 vintage fit fine. I dont know the backspacing of these though. I had a pair on a 69 Dart with an 8 3/4. They fit fine.
I also had a pair of WIDENED rally wheels, 15x8 in the rear of my own 67 Dart, also fit fine, using a 255/55/15 tire. It was an oddball size, but looked great and fit without rubbing. Both cars had totally stock wheel tubs, ZERO cutting anywhere.
If I get the hankerin' to use nonstock, wider wheels on an unfamiliar chassis, I do the following:
Set the car on jackstands, positioned under the rear axle and under the control arms. This will allow the car to sit in a position similar to being on its own tires. I take a stock rim without a tire on it and see how much clearance I have. Then I look to where I can add width. I try to keep 3/4" of space at a minimum from the tire sidewall and any suspension component.
The 67 Dart I had was equipped with an 8 3/4 axle from a 68 Coronet, so I had to have the rear wheels MADE to the size that I wanted. This did allow me to fit a wheel much wider than stock.