Yeah a .21 will fit. It'll be a bit tight, but it'll fit. Do a websearch for Wolfpack radicals, they sell a .21 conversion kit, a wise investment. About the drivetrain: after the first few "wot" pulls you'll need new diff outdrives and probably new dogbones. Maybe even a few gears. I know I did Hehehe...Ok back on subject.

Also look into RRP gears, they make metals ones to fit. Also you'll need to do a major upgrade on your diffs to handle the torque. I just dropped in new kanai diffs with the Hpi gear. it takes a little work but can be done. Another view point is to just buy a monster truck and convert it to a stadium (ie rear wheel drive)... Of course if your like me than the money pit is a good place to be. Be warned though, your truck is not meant to handle that type of power, and when you go out to play, stuff will break "EVERY TIME YOU GO OUT"... That being untll your whole truck is metal.

Now that your warned, go have fun!! I do