That big upper plug is the back of the cooling system- - - -the lower one seals the camshaft bore. A little bit of brush-on gasket sealer like Permatex Super 300 is a good idea when installing the new plugs.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!