I use marvel mystery oil for stuff like that. just get an oil squirt can, fill it up and line the walls. Then manually turn the crank to spread it around. After you put the head on and are about to fire it up again, repeat by squirting oil through the spark plug holes. Manually rotate the crank (plugs out) and that will recoat the walls and help protect the engine during start up. You'll get a little smoke at start up, but it works well.