8 3/4" rear axle? BBP with drums?
You shouldn't have any spring clearance issues at all with 275/60/15's and 15x8's with a 4.5" backspace. You will get a little close on the quarter lip, but that will depend on how low your car is. If that's the car in your avatar, it shouldn't be a problem. If you lowered it you might need to do a little work on the quarter lip, but 275's fit pretty easily on Dart Sports/Dusters/Demons.