When I was a kid, I mounted one of these...
onto one of these.
My friends dad turned axles for us out of steel rods. We used wheels from a red wagon. The front axle was mounted to a 2x4 that pivoted on a center bolt. A rope tied to both ends of the 2x4 provided steering. No brakes. Throttle lever mounted on right side (like a boat). Bright floral cushions. Fast as hell. Lasted three days. What fun!