318 in a 67 Notch???
Interesting you should ask that question. A couple of months ago I bought a 67 notchback Cuda off eBay. Guy claimed it was all original -- and he also said it was 318 in the listing. When I got the car and started to question him that a 318 was not available for that car, he came up with all kind of different stories. It was made with a Canadian engine. Other excuses came up. The guy was adamant that it was a 318, then he started to blame me for not doing my research. I wanted an original car, but I consider an engine swap kind of a serious change.
He also said that it had only one area of rust, and that was a whole bunch of crap. Look for areas of rust -- under the hood and in the trunk under the mat.
Anyway, the car starts in less than 1 second (which I really like) so I'm fixing it up. Bottom line: it is nice looking car.
Incidentally, I did some research and found a really nice original looking tire. It is a Maxxis 195/75R14 with a 3/4" whitewall available through Coker. It is a radial, fits on the 4.5" wheel width, and costs $83 per tire. Good luck.