I'm going to take a SWAG and say 23 spline in 1965 and 18 spline in the Hemis and a lot of 440 after 1966, maybe not My thinking is based on the NP833 being used the first time in 1964 and the little SS tires would spin a lot back then and not really strain the trans very much

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)