One thing I learned from the first (only) time I tried to adjust my 216 while running was that I can't do it.
I couldn't keep up with the truck even though Grampa never shifted out of first gear...
Actually what I learned was that it was a great way to find out that my rocker arm tips were badly grooved. They chewed up the feeler gauge right quick.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission