Cylinder 8 not firing

Put a new plug on the wire and got a spark outside the hole.
Then installed the plug and still no firing of the cylinder.
(apparently I should not do this again!)

I do have a spark.

Guess if I can find a leak down kit, that might help show me if there is a vacuum leak on the intake.

By chance are you using any anti seize or are have the plug hole threads been painted on the head? Plug wire arching on manifold?