If you have a later Plymouth and were curious - these are lists of all the sales codes they used. I think they go back to 1982 or so; they might even go back to the late 1970s, I haven't done enough research to be sure. The transmission list is of course much shorter!
https://www.motales.com/cars/materials/sales-codes.php
https://www.motales.com/engines/transmissions/index.php
It's kind of off topic but while we're here, this is where I keep articles showing Plymouth and other Chrysler Corp ads, brochures, press releases, and such... :
https://www.motales.com/chrysler-corp/ycats/lit.php