I had the same issue on my Hemi car that was just rebuilt and after driving myself nuts I finally followed the advise of a friend who had exactly the same problem with his Hemi.

Make sure everything is good on the top end, lube the crap out of the top end with cam lube put on the rocker covers and fire it up.

The top end is the last thing to get oil and on some race cars the oil passages to the heads are blocked off or restricted.

If you have a hydraulic cam and you don't have oil you will know within about 30 seconds.

The #4 cam bearing and the holes in the block are lined up at about 120 degrees intervals if you have 2 lined up it is really difficult to have the 3rd one blind.

I finally bit the bullet and fired the car up and there was oil on the drivers side almost immediately.

Anyhow that is my story.

Best of luck