As much as I like making stuff this is the easiest route. Bolts right on, probably a little better chassis balance with a bit less weight at the rear and to one side of the chassis.

If you want to convert though have a look at this build.
http://www.rctech.net/forum/monster-...0kv-build.html

The trans was converted to single speed with a couple of pinion gears and also has a standard forward only conversion. So the truck doesn't need reverse or the mechanical brakes and using the esc/motor for that like any other electric vehicle.