Zongshen or lifan 200cc or 230cc are very, very good engines that will easily bolt on your 200X. 5 speeds, manual clutch. Some have kick starters (not good as they are backwards), all are electric start.
They put decent amount of power 15-17hp depending on the specs (I like OHC motors), very comparable with the 200x's engine. All are not equal, but chinese engines will do you good. Prices have skyrocketed on those engines, but you can still find them new for what a used 200x top end with new piston and gaskets will be.
You wont be disappointed. You still have a complete rolling chassis to re-build with your kids, plus installing whatever engine you choose + all the wiring. Still plenty of work if you ask me.
Go ahead, do it!
Enjoy.
TORKER.
THOSE WHO SAY IT CANNOT BE DONE, SHOULD NOT GET IN THE WAY OF THOSE BUSY DOING IT...