The engines of yesteryear were pretty simple, with tappets clackity-clacking away on cam lobes, opening valves, and making a ruckus while doing it. Mechanical lifters were adequate for valve operation ...

When adjusting hydraulic flat-tappet or hydraulic-roller lifters for proper preload on a 350 small-block, a 454 big-block, and other displacements and engine makes with non-positive-stop stud-mounted ...