643 HP at the wheels, then......

Sorry to see this.
Are those pistons the 2618 alloy for boosted applications?
Or are they the 4032 alloy for NA.
Looking at the pics, it doesn't seem like much surface area retains the piston crown (the part that broke off) due to a combination of the dish, valve relief and ring land. Also looks like sharp edges on the transitions to the dish and valve reliefs might have made a hot spot that promotes detonation.
While the lack of meth induced this, whats everyones opinions on deburring the sharp edges and coating the piston tops? Do you think the piston would have survived as the weakest link should be the head gasket.
Best of luck to 70wayfarer for a speedy recovery.