I'd trust Linc's input on your gearing - I was just guessing on the compatibility of the tranny parts.
I checked Dafni's thread, and unfortunatley, his pic site is down or something:
http://www.rc-monster.com/forum/showthread.php?t=20384
Mike DOES have a file to make the mount he used, so that is an option.
I looked at BITHEADS thread on his HFX/Brimstone build and he used a Hellfire CD with an aftermarket Tamiya motor mount. Not bad....post 24 is where he talks about the mount.
http://www.rc-monster.com/forum/showthread.php?t=18633
He also mentions something in his thread that I found interesting, but being new to Savage, I'm not sure what it means. BitHed add some "new" savage part that allowed him to lower the roll center. Seemed to be something in the upper arm attachment. Anyone have any more insight into what this is?
I guess Finnster answered your question.....