I realize that this doesn't answer your question but first gear in a three speed is higher than second gear in your 4 speed. Reverse in the 4 speed is the same as granny which is great when you go to back up. In the three speed, reverse is the same as first gear which is pretty fast. It seems like every vehicle I had as a kid was a 3 on the tree and I always wished that it was a four speed. I swapped out the 3 speed in my truck for a sm420 and it is like driving a completely different truck now. That is just my opinion but I would never swap a good sm420 for a three speed.
