My opinion
1) lucky you have spare head, so swap all the valves and whatever in it as required.
2) find single piece piston (lowest cost)
3) if previously did not change rings, change it all now. Only RM95 for the full set. Else just change the single damaged unit
done - don't think about it anymore.
re-torque everything according to manual.
Bill Sherwood says every remember to oil the bolt thread and hole, but everyone forget to oil the surface where the bolt touches the limit. How to explain.... oil the whole god dam bolt.
When torquing use extreme patience, if torque value require 30 lbs, set 15, 20, 25, 28, 30
each torque turn 30 degrees only. move on and come back, very very little slowly
Clearances must follow.
No more upgrade required.
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