So the autopsy is finally complete. I doesn't look like the head gasket was pinched into the chamber, but it was perilously close most everywhere, and ultimately, I think the bore of the gasket being too close to the chamber was the cause.
Pic #1: breech at the water jacket at roughly 4:00, #2 cylinder.
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Pic #2: deck surface shows the print of the gasket, and how close it was to the cylinder. I measured it at 4.40, bore on this 400 is 4.380. Too close! You can see the hot spot at about 5:00 here just below the jacket hole that failed.
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Pics 3 & 4: Plenty of water in the oil showed itself mostly in the valve covers and oil pan. The crankcase looks surprisingly clean, if not perfectly clean.
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No other issues were found. Plan is to re-assemble with bigger bore, thinner crush head gaskets. Wish I could afford to do some headwork while it is apart, but I'm short on spending $$$ and just want to get it back together so I can get out at least a few more times this year.