[B. W.]

I've adjusted lash with the engine running, nothing wrong with that method but IMO you get better results with the engine off. Pull the covers & the plugs, set on TDC #1 on compression stroke (intake valve was the last valve to close), adjust intake valves on 1,2,5 &7; adjust exhaust on 1,3,4 & 8. Rotate 360° #6 TDC on compression stroke (intake valve was the last valve to close), adjust intakes on 3,4,6 & 8; exhaust on 2,5,6 & 7. Done with one revolution of the crank.
to get the proper lash, adjust rocker to zero lash, you can spin the push rod with your fingers to feel this. Then tighten an additional 1/2 turn (there is room for play here, some go less, some might go more, if you want to get real picky you can count the turns until your lifter bottoms & set pre load in the middle, I don't like bottoming the lifter to count turns so if I'm building a motor I'll use an old lifter, otherwise I just go 1/2 a turn)