For what it's worth,
I've been struggling to the get the (baffled) oilpan removed from my 360 engine in the car for almost a day (baffles, headers, steeringlinkage, K-member issues), removing the windagetray and oilpump, only to find out the pump was already an HV-pump!
I should've made better notes when I put this engine together.
So the cause of my low-pressure readings has now really shifted to elsewhere in the engine (first suspect: the lifter oilbands and lifterbore camfer).
I opened up the oilpump and found nothing but goodness inside. I will still install a new oilpump and fix the oilpan's baffles which got bent a bit by the removal of the pan.