sherman and other trannies like hupp and and F&T are pre tranny.
there are post trannies like howards and everetts. the post trannies can change ground speed in respect to pto speed. the pre trannies change everything.
are you saying you have 2 controls up front of the tranny?
post some pics.
howards are the maker of the rotovator / tranny combo.. that's how you can do a tiller setup with an N