Today I measured my clearances, with my 15" X 4.25" backspace and a 215-65R-15 roller tire on the wheel I have 9/16" clearance from the sidewall to the leaf spring.
Going outboard there is no clearance issues. It looks to me like I need a 15" X 8" X 4" backspace wheel which appears to me to require a custom made wheel. I can get an 8" wheel with 4.25 backspace off the shelf but I don't know how much tire I could get on that and clear the springs. I will be buying new wheels for the rear of the car and I will have two powdercoated 15" LBP 4.25" backspace wheels for sale. Need to get this right-glad it's winter I would hate to be trying to solve this if I could drive the car----:-)