If the close oil pickup was restricting inflow, then cavitation could have occurred in the oil supply flow to the pump, and put bubbles into the oil supply. You would likely never see this on the pressure gauge. But I would expect the rod bearings to be as effected or moreso than the cam bearings if this was the case. If the other bearings looked good, then I'd blame the cam bearings themselves, or their original installation. As MO notes, old bearing materials will deteriorate.
