I'd suggest finding a welder, and reinforcing the neck with a tube and reinforcing the headset where the cups go in. If you reinforce the neck on these things, it will ovalize the headset. I did it to a custom frame a sponsor built me.
Also, so you don't go through a bunch of read axles. Get a double armed fork, instead of running the "leftie fork." Another good tip, drill out the rear axle hole of the frame and put a 1/2 inch axle on, this will also require the bearings from a Go-Quad. Which you can also buy seperate.
KC Corning and myself were super into these back when Goped was an actual sport with race/freestyle events.
I'd suggest a stem and bars also.
These can be a lot more expensive than a scooter, but it's pretty fun. As long as you can flip flop from scooter to knowped, otherwise, you might be better off without one.