adjust the distributor to highest vacuum
Since that's a "no load" condition, it's frequently too much when loaded.
W/r/t valve lash with solids.
Regardless of what figure is used, the purpose is the same: that the valves always close completely no matter what the load, RPM or temperature is.
Subtracting lash (in the hope of improving peak power by extending the duration) is only as safe as the limits I just gave. If the valve stays open, that cylinder stops working.
Adding lash to reduce duration makes some difference, but also increases lobe/tappet wear (and noise) significantly.
