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?
i dont run the alterkation kit, but i have tubular UCA & LCS's. Currently im running a 245/40/18"s up front and 285/40/18"s in the rear. I can fit more tire on both but i played it safe since my first time with running the wheels and tires. a 255/40 would probably fit better on the wide rim up front but may needs some trimming to the fender, a 275/35 would probably fit as well. i can fit a 295 in the rear and still have clearance. but i think much more then that would be a stretch since i am on hotchkis leafs and dr diff offset kit. Unfortunately i dont have any good pics since the car is still in the garage, hopefully i will have it running in the next few weeks (never thought to upgrade alternator when i went to efi so car wont stay running because of voltage drop below 11vdc......im an idiot...LOL) and a poked a hole in my radiator so yeah....

20170321_145138_zpsfk8gw9gx.jpg

20170321_145120_zpshy4pliwt.jpg

I know 18"s are not everyones "cup of tea" but i like it........ so :p