Swapped heads on my 71 small block, just got it running and noticed that #5 intake pushrod and rocker are not getting oil. All others are oiling, the #7 and #8 have a small geyser coming out even at idle, while #1 and #3 take a few seconds but seem to be ok. When I had the engine apart I pulled all the lifters 1 at a time and looked them over, they didn't show any signs of abnormal wear. Rocker arms and pushrods are new, but the old parts were in good condition when removed.

I removed the rocker and pushrod and the passages in them are clear. Tried connecting pushrod to shop air with the pushrod bottomed on the lifter to clear out any obstruction but no change. What could be causing this? If it were a cam bearing wouldn't more than 1 pushrod be affected? Is there anything I can do or check before I take the intake off again and pull the lifter? I only ran the engine for 30s or so, but I did this 3 or 4 times, which I thought was plenty of time for oil to make it up the pushrod if it were working normally.

Additional information:

Solid flat tappet cam (comp 294s)
Comp magnum pushrods
harland sharp roller rockers
MSD tach drive pro billet dist.

Going to try running the pump with a drill and priming tool to eliminate the distributor as a problem next.