Thanks guys. I'll pop the plug out. Knock it out from inside the engine or knock it "in" from outside?
If knocking it out from inside can I use the camshaft as a punch?
I'd start by drilling a hole in it, inserting a lag bolt, and try to pry it out. You might even use the lag as a pusher on the cam if the plug is really in there. Or just insert a drift pin through the hole and tap on the cam.
I am sure the cam has been used as a 'punch' before! My last resort... LOL
Yeah, your lifters had varnish rings on the bottom ends....
Edit to add: No don't knock the plug IN from the outside; there is a ledge there and you won't get it past that.... well, not without some real destruction.