Slicks with stock spring location? (I know I'm crazy)

I recently bought a pair of 15x8 steelies for the rear of my Dart. I'm trying to fit the biggest tire possible, preferably a drag radial or slick. But I have a dilemma, the largest issue being that I have stock spring location and wheel wells. The guy I bought the rims off of had them on his 71 Dart and said he was able to fit a 9 inch slick, so I assume the backspace is correct. But I'm still concerned about rubbing. I can't currently measure backspacing because my wheels are off getting powder coated. I know this type of question seems to get asked here weekly, but I'm just looking for some helpful answers from more knowledgeable dudes than myself. What have you guys fit in the back on an 8 inch wide rim? I can roll or cut the inner lip if need be. Thanks in advance! :cheers:
-Jacob