Thanks all with your input, I solved it with a conversion chart from tirerack.com: https://www.tirerack.com/tires/tiretech/45_conversionchart.jsp

Plymouth in '65 used 7.35 or 7.75-14 and 8.25 or 8.55-14, and as mentioned above the 727 used an 8 tooth drivegear. Using the Tirerack chart, I converted the 215/70R14 on my car (incorrectly stated originally that I was using 205/70R14) to 7.75-14 the original size. The factory 1965 manual calls for Green 20 tooth pinion for 3.23 gear ratio.

So now the search for a 20 tooth begins,

Thanks, Tony