OK. Here's the top end stuff.
You'll need a new:
Piston, rings, pin, clips, pin bearing, 09169-18006 washers, and sleeve.
You'll need to:
Measure the connecting rod little end bore. 23.04mm is your limit.
Measure the connecting rod little end lateral movement, while holding the big end of the connecting rod still. 3mm is your limit.
Rotate the crank and feel the crank pin bearing.
Rotate the crank and feel the main bearings.
Fix or replace the cylinder head.
Inspect the reed cage for cracks or other damage.
Inspect the reed pedal for cracks or other damage.
Inspect the intake pipe for cracks or other damage.
I'd still recommend splitting the cases to clean them out. Gonna suck big time if a piece of sleeve is hiding under the crank halves, and gets sucked up when you fire it up, and wedges itself between the new piston and new sleeve or somewhere else...