It would be unlikely you'll generate enough torsional force to turn the cam by hand when the valvetrain is assembled (you're fighting against a bunch of valve springs) And bear in mind that these heads are used on both front and rear wheel drive engines. The FWD engines run a water pump off the end of the cam via a belt and pulley (thus the lack of a plug there) The end of the exhaust side rocker shaft missing a cap is a different story - get in touch with the supplier and show them a pic of it.