there is only 3 moving parts concerning the engine.  the transmission is completly seperate.

the power valve is probly fine but will need a good cleaning.   so far you know you need a top end rebuild.
 

--------
a good full on engine rebuild  would need
- crank bearings and wrist bearing
-a new rod on the crank
-crank seals
-piston kit
- piston wrist spacers.
--------

pull the cylinder up and take a picture. maybe you will be lucky and be able to remove the wrist pin ok. 
-you can test the crank a little if you get the piston off.