Largest Rim Tire Combo for 68 Cuda

I have run a 275/50/15 drag radial on 68 cuda with 15x8 4,5 backspace. My rearend is centered with the Mopar offset spring hangers. I had some slight rubbing on outside fenderwells. My problem was I had Moser axles and went to 10x 2.5 B body brakes this changed my offset by about 3/8 inch causing the rub. You have to consider everything.