Head gasket getting oval?

Head lift is when some thing, often the intake though there can be other causes, literally lifts the head. Doesn't have to be much, just enough to release some clamping force on the gasket. I proposed that idea as the gaskets are ovaling out towards the valley, indicating that some amount of clamping force is being taken off the gasket in that area. Moper did speculate on detonation being the cause, and it's a good idea, though I don't think pressure rise from detonation would not act in a singular repetitive direction, it would go any where there was a weak point.

Reasons the intake can lift the head:

the angle of the manifold face is different than the angle of the head.

the intake bottoms out on the front and/or rear china wall of the block before the intake draws up snug to the head. That is why I asked how you seal the intake to the front and rear china walls, and how much of the bead gets squished out. If when you removed the intake, there was nothing left of the bead on the top of the wall, your intake is bottoming out.

The attached pic's are my experience, aluminum intake, iron heads. They were done 3 seconds into an 8 second 1/8 mile run.

Let us know what you find. Good luck!!