3 speed output shaft seal?

Hey everyone, pulled the driveshaft out the other day to replace the u-joints and I discovered that the rubber seal on the output shaft of my 3-speed is ripped completely. I've been looking online to replace it and can't exactly figure out what transmission the 3-speed is... what is the model name of the 3 speed manual that came in a 72 dodge demon with a 318? Thanks for all the help!