The biggest problem I see is the very first event? Once that occurred, metal transferred to cyl walls.
That metal never went away, thus reducing clearance. But what is worse, is it would not support good film streangth of the oil. Additional metal continues to build up until the failure that shut you down. At the first event, you needed to tear down, address the damage, and more importantly, find the root cause?
This issue is a tricky one to identify at this point? Being its masked over. I think being lean to a degree built enough heat within the piston, to allow it to expand abnormally. That compounded by the cold water, not allowing the cyl to expand enough? I don't feel you were critically lean tho. I'm not able to identify any trace of deto in the pictures?
I recommend tearing down, and repairing the cyl. ( clearance to Oem specs). Adjust jetting to what I recommended earlier. Continue to restrict cooling water as you were doing. You were on the correct track. Monitor motors condition as you break it in, and adjust as necessary.
Keep in mind all I'm suggesting at this point is a known (to me) better jetting spec than what FPP initially recommended. You still have not identified the root cause? You will need to back track the issue until you can identify what had happened? When you rebuild the top end, make sure you do a leak down ck? Make sure there is no cooling water leaks that could "Mist" the carb intakes?
Pay attention to details
