Prime the pump. Did you pack it with Vaseline?
Here's a trick I have used.
Remove the sender unit. Seal either the oil fill or the dipstick hole. Apply air presure (no more than 20-230PSI) to the other hole while someone cranks it with no plugs. s the air pushes down on the olil, it will push up through the pump and out the open port where the oil sender was.
If you do not remove the sender, the air pressure pushes down on the oil, and in at every place the oil would squirt out, like rods, mains, rockers.
Always worked for me in those kind of situations.
30 seconds, if it doesn't work, something else is wrong, like the pump drive not working.
To pressurize oil fill, roll up a shop rag, wrap it around your nozzle and stick it in the hole.
PURPOSEFULLY not a tight seal to cause main seal issues.