I have a 69 chevelle with 15" rally rims. The rear tires ar MT Indy Profile 60's (poly) and the front tires are ?? p215/70 15 (radial). I realize that I need to change the front tires to poly and will look for MT tires in the same size. If I change to 60-70 SS 15" repro rims what rim spacing (15X7??, 15X8??)would I have to order?