I have done this and it is not an easy thing. The original motor mount requires you to cut a new slot in the chassis which takes some effort. Also it requires that you mill the area for the motor to sit lower than the chassis surface. The center shafts fit fine.

1) Major chassis modifications or new chassis
2) Battery mount modification is major
3) New top plates are required even for this modification

In the end the Schelle chassis with their kit, once available, will be a great solution for those that don't want to jump to the B44.3 kit. Add the new gear diffs and you are almost there. This is my plan right now if I don't want to just take the plunge and jump to the new kit.