If I buy a sfi case for a TH400 will my stock case internals be usable?
Does a roller bearing tail shaft require a different yoke or drive shaft length than the stock bushing type?

You will need a hardened yoke, not sure about the rest

I think everything will work except for the center support and intermediate clutch pack. You have to have one that's made to fit the case because it has lugs all the way around the case. Not 100% certain on that though......