Piston Failure

Better you blew a head gasket than one of your pistons, for sure. I wish that was what happened to my engine instead of the opposite, I was also running Fel-Pro 1008's IIRC... no matter my current engine is better anyway, Cometic head gaskets with ARP head studs holding down ported Edelbrocks.

Definitely get a wideband O2 sensor on there and check the plugs frequently. And machining the decks is a good call.