If you didn't seal the ends you'll need to. It's sucking air. Use a propane torch and direct the gas at the easiest corner and the idle will smooth.

Propane test was negative, no change in engine. I think it may be a bad spark plug gap. During the whole head gasket assembly process, I remember seeing one if my spark plugs had been squashed between parts and bent the lead down. I just eyeballed the gap one that one and reinstalled them all. That could be the issue

If you are sealed the misfires may well be plugs and or wires. I'd replace them if it's been a while.

Agree definitely. With this kind of job it's good insurance unless you know they're almost new.