the lash on the stems is some thing you can do , just take a marker pen , black the tips of of the stem tips , place your rocker assembly in place adjust the lash and rotate the motor a few times without plugs in it . then inspect the stem tips , should have a mark straight acrossed them in a line right through the center of the stems . low of center is not great , but high of center can be lead to damaged parts and major damage to the engine . that just the start of the set up .