[ford38v8]

You won't get a steady pressure reading on a gauge between pump and carburetor, as the carburetor's needle valve will open and shut as required. An accurate reading can be had by capping the Tee and supplying the carb with an independent source. Pressure specified is 3-4 lbs, but should be fine with as little as 1½ lbs. Higher pressures tend to open the needle valve too much.
On a side note, save the old pump springs for possible use in new pumps, as some new springs are stronger than spec.