Standard wheel in 65/66 (and maybe in later years as well) was 13 inch with the 6.50 x 13 standard; 7.00 x 13 optional. Formula S (and possibly Darts equipped like a Formula S) got a 14 inch wheel shod with a 6.95 x 14 tire. So yes, the 14 inch wheels for those years were pretty rare. For the Plymouth, there were 13 and 14 inch Formula S-style hubcaps with the 14s being pretty hard to find in any condition.
I see that you know about the Formula S 14 inch hubcaps/special lug nuts I have for sale here on FABO - http://www.forabodiesonly.com/mopar/showthread.php?t=126769 - not sold yet. I wasn't thinking about the wheels/tires (195- 70 x 14) that on on the Valiant now, but guess I could move the car and get them pulled off if need be.