Check it with a straight edge. You will find most wheel wells like that. My 64 Belvedere is that way
I haven't had a 66 or 67 Plymouth since 72. It did have americans on it and the tire was close to the lip. What you may have to watch for is like my Challenger. The lip is the closest spot. But only the very rear of the lip where it turns down towards the bottom of the quarter panel. The rest isn't a factor. You are blessed with the smallest rear wheel weels of any B-Body. Good luck.
Doug