I use a spark plug shell with a piece of all thread tapped into it as a "head-on" positive stop. On a stovebolt engine the rod needs a 45 degree bend in it to get into contact with the piston and a lock nut on top of the plug shell.

One round track roller cam on a 350 had a quick enough rate of lift that the closest piston to intake valve clearance happened at 25 degrees ATDC. That one was running 1.6:1 ratio rocker arms and it needed a rev kit to combat valve float. "Idle" speed was 2000 RPM. Below 2K it didn't load up or lope, it just quit running. It smoothed out at 3K and it was still building torque when we quit doing dyno pulls at 7500. It would come off the #4 turn at 3K, and accelerate all the way down the straightaway of a 1/2 mile banked oval.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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