1968 BARRACUDA WHEEL & TIRE OPTIONs !!!!

I recently bought the Alterkation kit with the Wilwood brakes. I'm very close to installing them. However, I can't go stock anymore on the wheels. Their recommendations is a wheel no smaller than a 17". I would prefer going with a 18" since there are more options on tire sizes. Does anyone know what is the max diameter and width on the overall size of the wheel with the tire without going crazy on adjustments or cutting?