I'm changing the scale to 1/2, because I need a little more room to fit everything, and myself. I might also look at doing some form of suspension, just because going 35mph over bumps/potholes could get uncomfortable after a while.

And the 670cc V-twin isn't feasible right now, because the clutch I would need costs more than the cam, billet con rod, and flywheel for the 212cc Predator. I'll just build it with enough space for bigger engines later on.