I own both of the 4WD and 2WD, but in a Ruckus. It's pretty much the same vehicle.
That aside, I'm not sure what other brands will fit. It depends on what you wanna do. I've been switching my shocks over to the Hot Racing big bores. I also went with a steel spur and hardened steel pinion for the drive gears.
Disassembly on the 4WD is a huge pain. After having to open it up more than I care to replace or adjust the slipper, I went with steel and just cranked it down.
Also, shim your diffs. Those are the biggest pain to fix. Ugh...