I have a 1970 Mustang with 4 wheel drum brakes. I have been looking at a complete 4 wheel disc brake kit from Wilwood. They are 12.19 rotors on all 4 corners. Do I need to be thinking of 13" instead? Will the 12" units work for what I want? It will only be for spirited road use and no track use at this point anyway. Thanks guys.