Melted piston caused by detonation.
Ringland wasnt an issue that model.
I would advise rebuild your own as cheapest option. as your crankshaft should/would be ok. Could add forged pistons and rods if needed.
Change fuel regulator and flow test injectors to eliminate that as cause.
And double check if vaccum popped off or was cracked.
This all related to finding cause and preventing again