Blown headgasket. What's next?

I'd tend to agree with you on that spot on #6. If you found some excess or deep scoring on those 2 cylinder walls, it might be a good sign of a damaged piston ring, broken from detonation.

The fire-ring bent out like you show is from a lot of pressure inside the cylinder. Normal warping of the head or just common gasket failure would not bend it like that; it'll just burn or blow past the ring. (From what I have experienced, at least.)