I always got asked if my shuvit was a rota au. when it was on 3 cylinders. so i say keep it like that
Test if there is spark getting to the plug.
Test them all again just to be sure.
Has the engine been sitting a while?
You cure powdercoat at about 200C. Not super high, so as long as they weren't cooled abruptly i would imagine it would be no worse than jumping on the brakes a couple of times