Thanks Jack.
I would add that I mentioned "old engine" because the underside of every rocker lash pad will have a divot in it that is far more than .0005 or .001 or even .002 deep. These are tractor engines, and the worst that can happen when adjusting is that they are looser than intended, and that's fine if they are at all quiet.
I reprofile the rockers when overhauling these engines, and with a new cam and lifters they are still noisy, but a "pleasant" noisy, not clattery.
I use the overlap method when adjusting myself, which is to observe two cylinders along in firing order for the overlap point, so when four overlaps, I adjust 1. And so on, because I don't have to pull the cap, or look at the marks on the crank pulley. That's worked for thirty years and about a gillion adjustments.
It's not a Porsche flat six afterall - close is good enough.