I think that using a TVP chassis design, such as that of the Savage would make things much more difficult for you. To my knowledge there are only two MT's out there which use this design - the Savage and Warhead. That limits the choices of trany and diffs, as the mounts will be completely different to those found on "regular" type MT's which do not use TVP's. And, as most Savage owners would agree, working on a TVP chassis is a nightmare as everything is wedged in there - the only way to get at anything is remove the TVP's.

Just something to think about - you don't want to make a custom build any harder than it has to be!