Re: My very first build
You will need a new back wheel with either a coaster or derailleur hub.
I do not think a GX-50 four stroke will fit. I would add a two stroke China girl to that frame.
-All things considered, I would keep your fixie as-is and buy a beach cruiser bike to motorize. The GX-50 will fit in a beach cruiser frame.
“You're only young once, but you can be immature as long as you like" -Unknown