Nice minimalist kart though with the simplest of frames, whatever it is. More photos of it, please. Since the rear frame is lowered (or raised as the case may be), the kart is slung low making it ideal for pavement racing. I'd put slicks on it in the same tire size and just go for it.
Nice Briggs too--a piece of history. Keep it as a new Predator engine (ugh) would look out of place on it.
Is it one-wheel drive?