www.tqrcracing.com
The usual upgrades are the vertical motor mount, 19t pulley, and the aluminum gear adaptor that allow you to use the 19t pulley.
Other good ones are the aluminum wheel hexes and titanium turnbuckles.
I would also get 1mm and .5mm spacers, c-hubs, steering knuckles, rear uprights and suspension arms just to have in the tool box.
It comes with a 48 pitch spur, but i've switched over to the 3racing 92 tooth spur in 64 pitch.