Smoking 273, opinions?

UPDATE.

So today I finally got around to checking inside with a scope. Walls still looked good and could still see cross hatch. To my surprise the pistons have valve reliefs which I did not know, so I bump the starter a few times to get looks at the entire bore when suddenly a big fat oil drip comes running down the cylinder wall! Check out the photos.

So before I pull this head off I’m thinking cracked head or valve guide.