Mountain bikes sometimes have uncomfortably quick steering at higher speeds. A shorter stem usually helps. A heavier front wheel and tire can stabilize the steering too if it feels twitchy at speed.
Ya, your gonna want a cruiser seat and cruiser handle bars because your gonna be changing the way your ride instead of leaning over the handlebars more prone vertical position much less effort.
100cc(80cc) motor with sbp jackshaft shift kit. Finally got her done. Runs decent but the first few times turning it over was hell with the pedals.. bought a pull start and rigged it up but it failed and I was lucky it didnt damage the magneto. Back to kickstart for now but not as hard to get it going.