Low oil pressure prob on a fresh rebuilt 1971 351w its around 40-50 psi but you know it should be a lot more you had this problem before and it spun rod bearing not sure what the prob is?

As a rule the early Ford engines had relatively low oil pressure! Cold start they run about 65 pounds then drop down as the temperature of the oil rises and is very common to have 10-15 pounds hot idle. There is nothing wrong with the engine, just the nature of the beast but unnerving just the same when you see the gauge hanging around 10 pounds but lifts only need 6 pounds to function and that seems to be all Ford was worried about back in the day. High output pumps help but seems to only bring it up a few pounds.