What back spacing are you able to get away with on rear discs? 3.5, 3.75?? Or do you have to do custom bs rims, spacers? What I have now is soa rear with GM disc conversion, tires I have are 35.15.5X15, trying to determine what the best rims are to run, with the best backspacing. Front is soa, shackle reversal, cut and turned housing with saginaw P/S. Another concern is the tires rubbing on the frame, or springs at full turn in the front. Any suggestions?