360 Oil Pressure Issues

So I can check for that oil plug by just pulling the distributor and looking for it?
No, that plug you referenced, you check by inserting a rod down through the sender hole. There is a measurable dimension that you check

Plug BELOW, posted earlier by George Jets is checked via the dist. hole. You pull dist, shine light down, and you can see the plug sort of "sticking out" towards the rear plug

screenshot_20210728-170122_gallery-jpg.jpg

MEASURING FOR THE SENDER GALLERY PLUG:

From here:

Oiling problem. HELP!!!
=======================================================================
From post 28:

I have an engine going together in the garage. The plug above the rear main cap can be measured from the top of the block. Use a long (at least 10') small rod and place it in the hole on the rear of the block next to the disty hole. This hole is for your oil pressure gauge or sender. Mine dropped in 7.7" until it hit the plug. Someone on here said 7.5". Its an easy way to check without pulling the pan
.
=====================================================================

The answers I found were sparce, the one above seems best. Seems that if the rod goes down further and certainly if it goes beyond 8", the plug is missing.