cooked it! What did I do wrong?

Was that AFR from a wideband in the car when it happened?

With a that piston @ +.060 you need chambers at least 90cc's to get close to where you should be. What was your combustion chamber volume?

92 octane pump gas can be all over the place as well. We are switching from summer to winter blend all over the country right now too.

If your spark was really close to the edge, and you got some 90 octane stuff, or some winter blend that lights a little faster...

Sorry to see any damage like that.

What does the plug look like?

B.