Ouch!!
I assume by checked out, you mean with a mechanical gauge right on the block?? Sometimes the senders are at fault, or so I've read.
Three basic possibilities: the pump isn't pumping, there's a blockage before the pressure sender (and therefore everything else) or there's an internal leak large enough to prevent pressure from building up.
In my experience with other engines, I've found the connecting rod beaings to be a more likely suspect for excess wear than the crank main bearings. Can we assume those were looked at and deemed Ok when the crank bearings were checked? Clean out the oil passages in the block? Filter not plugged AND the correct type? Take off the filter & crank (not run) the engine, does oil make it that far? Oil pickup connected to the pump correctly? Oil pickup screen not plugged? Pressure relief valve not stuck open? Pull off the valve cover & see if there's oil flowing up there.
A stupid silly question but so basic it's worth looking at: there's oil in the sump and the drain plug didn't fall out?
Best of luck,