360 engine sudden drop of oil pressure while cruising at 3200 rpm

Big block mopar you were right pushrod snapped metal fatigue, and was missing an oil gallery plug in front of distributor, motor is good now lots of pressure 80 cold 35 idle 60 cruise speed
Congrats on the fix! Just curious. How does an oil gallery plug get removed and not replaced? I don't even understand why it would have been removed in the first place. Seems out of the norm.