Ingo Swan, I know I've read the dates for the SM-420 but I don't remember exactly what they were as it wasn't important to me. Basically I think it was made for about 20 years, roughly from the late forties to the late sixties. If I remember correctly the SM-465 has a bigger cap diameter for the front input shaft bearing which means the hole in the bell housing has to be bigger for the tranny to plug into the bell housing. The bell housing can be machined to take the SM-465 which is even more heavy duty than the SM-420.
