Priobe,
No, I don't know if side oilers have that plug/hole or not.
Also, many of the above suggestions focus on suggestions like the plumbing might be too small, fittings might be restricting flow, the plumbing to the cooler might be wrong, etc. While all of these things are important, they won't cause low pressure. If I see your picture correctly, you're measuring the
oil pressure at the remote adapter right at the block, correct? If that's true, any blocked, undersized or reversed lines after the remote adapter will cause your
oil pressure to read too high (but with little or no flow through your engine).
Once you determine that your gauge is accurate, I think there can be only a couple of possible causes. Either 1) your
oil pump is not working right (they have a bypass spring in them that could possibly be stuck), 2) the oil pump is starving for oil (because the pickup tube is loose or the gasket is missing causing the pump to suck air or because the pickup is too close to the bottom of your pan) or 3) you have an internal oil leak. An internal oil leak could be caused by a missing internal oil galley plug or it could be caused by excessive rod or main bearing clearances.
What's the history of your motor? Is it an older motor with with some miles on it or is it recently rebuilt? If it's rebuilt, did you do the work or did someone else? How were bearing clearances checked?
Chris