Need Help! Low Oil Pressure

I have a very well worn 134 F Head in my 55 CJ5, When the engine is cold it idles with close to 40psi untill the oil warms up then it drops off close to zero on the existing dash gauge, the slightest increase in rpm over idle bumps the pressure up to a little over 20 psi instantly on a hot engine. This gauge records 0 to 100 psi in 10 pound increments, Not very accurate for checking questionable low pressure. I was concerned with this also and temporarily installed a more accurate 0 to 15 pound gauge, It reads just a hair under 5 psi at idle with the engine hot ( 160 degree t-stat ) running 10 wt 30. The Universal Service manual that I have lists 6psi as minimum safe pressure at idle and 20 psi minimum at 2000 rpm, there is no doubt the oil pump and everything else is worn some. I dont drive it very far or hard untill I can overhaul the engine proper because it has other issues like badly worn valve guides but I can say that I have been teaching my two girls and some of thier friends to drive in this rig and we have clocked up alot of slow stop and go idling on a hot engine with no problems, I even take it out and putts around in low range now and then. I agree with the others responding regarding flow rate vs pressure. If you are showing pressure on any type of gauge over 10 psi hot and idling I really dont think you have anything to worry about.