VIN number says 6cyl. but shows as a 318

Without a fender tag, it's harder to tell. VIN should also be on engine and transmission as well as a few "hidden" places on body shell.

A slant car that grew a 318 is nothing new. Nor is a car losing some of it's A/C. Somebody actually taking the time to stick an emissions/tune-up sticker on the car after a swap is a bit more rare.