Owen and I cleaned the carbon off the piston and the combustion chamber and valves.
I pressed / held the valve open by hand, while Owen used wire brush to clean the valve seat.
Carb cleaner did a great job, sprayed it in each valve chamber, soak.
Next weekend will re-assemble.
Need to look at the GY6 manual for proper alignment of crank rotation, placement of cam, etc.
Head gasket will re-use.