I had to do a double take when I saw this.

Dubob said

Maybe take an angle grinder with cutoff wheel, pop the head off. Once you pull the cylinder head off it’ll probably screw out with your fingers.

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I really don't see how it could be in there that tight, there are no marks on any of the edges.
First attempt I am going to cut a notch across the top, and hit it with a twist impact screwdriver.
Second attempt notch an edge and try to spin it off, with an air chisel.
Third attempt I might weld a nut to the top of the bolt.
I think last resort is cut the head off.