Did you eliminate bypass valve in oil adaptor housing or block? If gen6 the valve is 11 lb unless someone installed 30lb or blocked off totally

You should cut the oil filter open and see if there is metal again.

Like Force said use a mechanical gauge .. Mine goes used to drop to zero, replaced sender and gauge, no change. Mechanical gauge read perfect .... turned out to be a ground issue.

Lifters pumping down means to me no oil pressure regardless of sending unit. Otherwise I would agree on mechanical gage. I've had low reading senders before that were shown to be such by a mechanical gage.

Are you sure the distributor is turning the oil pump? Take the gear off and slip the dist into the block see if you can feel the pump by turning the rotor. If it works with the drill but not dist, maybe a short oil pump shaft????

I mounted a mechanical gauge on the transom, tee'd in the electric sender, any question I lift the hatch and trust the mechanical. With the sender on the transom, less vibration from the motor, supposed to last longer.

There is a major issue if you have zero oil pressure start with filter... If there's metal just stop and pull engine and tear down you will find the issue.....if filter checks go with the distributor thing... Start with what drives oil pump and move forward.....

Who built engine? Sure all clearances are correct? You spin a bearing you will have little to no pressure at idle... But can get some with rpm.... Like the other guy and I said... Cut oil filter tells a lot