I&#039;m surprised John hasn&#039;t replied.

On a 283 Gas, the only items under full oil pressure is the main oil gallery down the side of the block, the main bearings, the oil filter, and the Main Gallery bypass.  Rod Bearings catch oil and are not pressurized, rocker arms, cam, and timing gears are supposed to be intermittent.  I recommend, if you haven&#039;t already done so, use another gauge and check the pressure directly of the blocks main gallery.  There are little pipe plugs all down the gallery.

If the clearance is correct on the mains, and the pump was in good shape, then it could only be a few things.  One is the bypass valve on the main oil gallery.  Normally, it&#039;s at the front of the engine.  Two, oil filter is restricted, three, did you leave a rag in the pan?  It happens....

Are you measuring oil pressure off the main gallery near the rear of the block?  What was the pressure before you rebuilt the engine?  What were the main bearing clearances?  Did you dissassemble the oil pump?  How did the oil pump fit into the distributor/oil pump bore where it mounts?

There is a lot of questions to narrow down your search but we need a little more info.