15x7 wheels- fit 65 Cuda?
If you're willing to play with the backspacing a bit, you can certainly get 15 or 16s to fit, depending on how thick you want the sidewall to be. I went through a progression of wheels on my car, from the stock 13/185s, 215/60/14s, and finally to 245/45/17s, which required some monkey'ing with the backspacing on my rear.
I chose 17s only because the wheels were cheap, and there is a greater selection of tires available. If I had my choice, I think 16s would be the best compromise between aesthetics and handling, and avoids the rubber band look. Its not for some folks ;)

Stock 185/80/13s

Cragar SS 215/60/14 (4" backspacing on a 14x6 wheel)

245/45/17s on a 17x8 wheel (front required minor trimming on the inside front lip)
and a little small but you can see it from the rear
hope that helps.