help with priming

Check the notch on the rocker arm shaft and make sure its in right. If its backwards it affects the oiling. Notch goes down and you will have to do a search to see which direction it faces. Its opposite on one side of the engine from the other.
Its most likely you just are not lined up with the oil hole in the cam bearing. Easiest way is to have someone spin the pump while you slowly turn crank a couple degrees at a time. Wait a few seconds between rotations to give the oil time to get up top.
Worst case scenario is you had a chevy guy build the engine and the cam bearing is installed wrong (oil holes not lined up).