Do you by any chance have one on a compressor from The Cornelius Co out of
Minneapolis Minnesota? The compressor is a 130RO300-8.

I was told it was last being used as a scuba tank compressor, but it was
previously used for aircraft circa WWII. This one has a small gas motor to
drive it.

I'm trying to determine its max operating pressure so I can see if I can use
it to fill my airguns or better yet my SCBA tanks that I use to refill my
airguns in the field.

If its only SCUBA pressure I can still use it directly as none of my current
guns uses a fill pressure over 3100.