I have a new old stock AC 4149 for comparison.
My guess is they used the wrong rocker arm in that problem pump.
Look the gap at the bottom (pivot). There is a lot of the pin showing.
Attachments
Pump 01.jpg (59.43 KB, 111 downloads)
Pump 02.jpg (61.25 KB, 111 downloads)

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."