Have you thought about getting rid of the trans and using a center diff with integrated motor mount (like this:
http://www.rc-monster.com/proddetail.php?prod=rcmcdmm)
That stock blue motor plate on the trans doesn't look like it would hold up for very long with a 2217 bolted up to it. Center diff design would make the setup a lot tougher.
Welcome to the forum, look forward to seeing this thing completed!