John check this link, it might help
http://members.cox.net/cglabe1/SM420/sm420.html I had a problem to get the clutch shaft in when I did it. Lots of heavy grease to hold the needl bearing in and also I think I remember that I had the gear assembly the wrong way around.
My memory some times fails me, but after dropping the trany on my thumb , my memory cam back, also it gave me a nice blue finger nail.
