Largest rear tire size

I have 9.00-9.50/14 M&H cheater slicks, 14X6 Cragar GT wheels on my 1966 Valiant, they are a tight fit but fit fine. I may trim the inner fender lip a little, I would bet if I hit a big bump they might rub. I also have a pair of steel mopar 15X6 rims with 255/60 15, those clear just fine! I think I could get away with a 15X6 1/2, a 15X7 may be too much with that tire size! Oh, by the way, I have super stock springs and drag shocks! :burnout: