Frank, Looked at all the options for years and because I have a PTO attached to my sm420 I was pretty much wed to it. So, opted for a gearvendors. There is an adapter that bolts to the sm420 followed by the gv unit, followed by drive shaft shortening. Works very well but let me tell you. GV doesn't give anything away. I actually drove the 100 miles to their factory and spoke with a rep. They were not bashful about taking my money. There is a 5 speed that is a direct replacement for the sm420 that they had in their showroom. Can't recall the #. Don't know the price. Probably nose bleed territory as well >(
