Low oil pressure when warm, Crushed. Finally get to drive the car and the idiot light comes on Options

[trojanhorsepower]

A bit of background.
My engine (short block) was assembled wrong by a "professional" about 23 years ago before I got it. When I got it I finished assembling the rest of the motor and found the cam timing was wrong. After several posts and help from Jake Raby we found the cam gear had been installed backwards and a new hole drilled to make it fit. At that point Jake had me split the case, mic the cam and crank and get the numbers off the bearings. All that checked out. I rereassembled the engine and everything went well. Now 23 years later I have the engine in the car and it runs pretty well. (using Brad Penn 30wt break in oil) Except the oil pressure idiot light comes on at idle after the engine warms up. Maybe 10 min of driving. Now based on the threads I have read and the books I have there are no components that affect the oil pressure once the oil is warm? The check valves are for cold oil correct? Hot oil should just bypass the oil pressure bypass valves?
So I will change the oil for 20w50 VR1, but really am I just grasping at straws? What can actually cause this other than bearing wear? An out of spec oil pump? Anything else?

Thanks for the help

Peter