If all you want to do is a valve, injector set, then just follow the instructions in your manual. Otherwise leakage is pretty much guaranteed once its all back together again. If you disturb an old engine to change these, you must pull the housing end plugs to renew the 'O' rings. One gasket choice has to provide a satisfactory average for two cylinders. Different thicknesses of rocker box gaskets are available to move the low mounted rocker rollers in or out of contact with the cam lobe. Your manual will no doubt show you this, but one dial registers via a long stem through a removed injector hole the piston position relative to crankshaft rotation, while another registers the push rod travel. If you're wanting to check 'injector timing', you'll have to locate and use one of the traditional dual dial indicator tools unique to Cummins PT fuel systems.
