How much RPM does it take to raise the pressure, and what pressure does it have at 1500 RPM or so? Also, how extensive was the "rebuild"? If the engine was not removed from the car, and the cam bearings changed, they can be the source of low oil pressure at idle. In the early 1960's when the 55-56 265's started needing to be rebuilt, we discovered that an "in the frame" rebuild without changing cam bearings was not a good option. Those engines would make the idiot light flicker at hot idle, which meant the oil pressure was under 7 PSI.
Jerry
