Valve lash

Correct! Once you pre oil the valve train will become oiled. Lifters pump up and it will do its thing.
I started with the chart and corresponding valves, spinning the pushrod until a slight drag was felt then, I used a digital gauge on the cup to the valve cover lip, then 0 the gauge, then between -.015 to -.020 with the adjuster and tighten the lock nut. It turns out to be 1/4 to 3/8 of a turn. It worked great at the dyno and in the car. No issue at all. The lifters can have some tolerance between valves and they may make a lil noise when you 1st start it until the oil psi builds up in them. Header leaks can sound like they aren't adjusted right too..