What MT 2 do you have the RTR or the SS? If you have the RTR you nee to up grade all your drive train to SS. When I did mine HPI did not have the new diff cases but if I where to do it now I would try them first as GPM parts are junk. When I did mine I had to use the poorly made GPM case, as that is all that was available.

The TZ will have no problem making your MT over powered and you will break more parts! I had to gear mine WAY up just to keep the wheels on the ground MOST of the time. As far as which one depends on what sort of carburetor and starting system you want. I will tell you till you get the TZ broke in with a pull starter get ready to fix it numerous times as the pinch is very tight. All so use a heat gun for break in.

You can use either one with a standard or pilot shaft. The older MT before the 3.0 used a standard shaft and the 3.0 use a pilot shaft if I am not mistaken. But you can make either one work.