Love the oak bed. You created a sweet little RPU!
It looks like it was a pre-existing go-kart frame that had a little caster angle in the spindles. What did you use to form the hood? I like how it covers about 300 links of chain, that would otherwise grab ahold of whatever tender bits were available.
By now, I'm sure you're aware that a 200cc pushrod China motor is just about a bolt-in deal in your kart.
As well, there is a driveshaft option, with reverse:
http://item.taobao.com/item.htm?spm=a230r.1.14.100.b1DbjQ&id=7930135107 That's about US $27.00.