Is 5lbs of oil pressure to low for a warm rebuilt 80 model 350 with a mild cam?

Yes, 5 lbs. is too low and you should look into what is causing it. Could be worn bearings, light oil, missing oil passage plug, bad cam, bad pressure gauge, etc. 5 lbs. of oil pressure is very low ,unless you are at an idle, and the engine idle is low. is 5 lbs. what you have at 30 miles an hour? There is no question that 5 psi is too low for a newly rebuilt engine, now the questions start: Who rebuilt the engine? Was the crank turned? Did a machine shop test the block to see if it needed to be align bored? As the above question hinted, what was the engine RPM when you were getting 5 psi? TYPICALLY (assuming the engine has been assembled properly and the oil pump is functioning, pressure bypass has been assembled properly, main and rod crankshaft journals are "round", rods have been reconditioned and all of the other machine work has been properly completed...) low oil pressure is caused by too much pressurized oil leaking past the main, rod or cam bearings. That is caused by an excessive gap between the bearing and the crankshaft. The bearings ride on a film of pressurized oil and SHOULD never actually touch the crankshaft if everything is working as designed. IF the problem is worn bearings, out of round rod 'big ends', worn oil pump, etc, you can OFTEN raise the oil pressure by changing to a higher viscosity oil. If you have been using 5W15, change to a 10W30, etc. If that puts the oil pressure back to reasonable mark on the gauge, you know it's wear related. haha yeah u should have between 40 and 60 at least