I'm thinking the 3 wheel option would be the best. You start with a scooter and chop it in front of the motor(easier said than done) then a 2 wheel front end that has one of those differential gokart axels. Steering would have to be like a front end loader and bend in the middle. Seat low and right in front of the motor/steering joint. Pedals in front up kinda high to clear the axel, Steering by solid rod from tillers attached to the frame. The tiller handles hold the engine controls. Biggest problem is it would be a bit "tippy" but no worse than one of those Polaris 3 wheeler bikes.
I can visualize this, I'm sure many won't be able to but it answers all your criteria and would be fairly easy to fabricate....if you have those skills