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?
What? I have a 68 Barracuda with the RMS front suspension and Wilwood brakes. I run 15x6 Pro Star wheels with 215x60x15 tires. Works great.