widest tire for rear 68 cuda

I have the disc brake conversion but I believe they are the early K-H disc setup and the wheelbase is still stock , but I could be wrong I just know that you risk a problem if the lips aren`t rolled on the front , I have seen the wheelwell moldings trimmed on the flat side and rolled up the inside where the lip is rolled on the fender but thats a tricky one to pull off .