I used everything from the Mugen MBX5T..The chassis I'm using is a BCE Mugen 5 XXT..I got the whole center diff set up on ebay..it was cheaper to do it this way..The BCE chassis is a bit longer than the Caster chassis..Going to the smaller spur gear does make a huge difference in acceleration, and it does move the motor closer to the center line, lowers the weight a bit, puts the drive line in a better angle also. I'm still working a few things out but overall the Truggy is 100% better than it was..I got rid of most of the bump steer..easy fix also..makes it track so much better through the blown out sections. I am using the Mugen out drives on the diffs but we had to do some machine work on them to make them work..I'll take some photos of this. I think the Truggy has to much caster in the front..I think it's around 33 or 34 most of the other truggies are in the low 20's..Makes for a very stable truggy but it does not make a quick turning truggy