yep, look at the gearstack worksheet in the how to section. It will give you all of the gearstacks that have the same final drive. Any of those can be swapped into each other. If you want to use the 4.0 final then you would like Miko said have to replace all the components on the stack of the mainshaft. Imput shafts and gears can swap straight over but you would have to have the gears switched over to the old mainshaft. Simple as that.