How to destroy stuff . . . .
Most HE pistons to not handle detonation long enough to look like this, they most often stick the ring pack and pull the bottoms of the pin bosses out and the rod / pin combination saw the block in two!!
I have never felt that modern street fuel (any of it!!) would support much more than 9.5 or so with way short timing (those Vortec heads should not need much timing).
Not sure if the HE pistons do this, but most forged pistons will shrink slightly when you detonate them, that may try to stick the rings in the grooves. And once you pinch the ring lands, oil enters the fuel / air mix and lowers the octane the motor is seeing even more and compounds the problem / damage.
No head gasket leakage?? No "Pepper Specks" on the spark plug porcelain?? That would also indicate detonation.
Take care, K