Not sure if this has already been covered here, but just spinning the oil pump won't get oil to the rocker via that oiler hole. The cam must also be turning (unless you're very lucky and it happens to be in the exact right orientation).
I had a similar symptom as yours when trying to get oil through the head on my 79 that had been sitting for many years (dry rocker assembly).
After determining that my head gasket was oriented properly (supposedly it can be flipped 180° and cover that oiling hole in the head), after verifing my oil pump was pumping (filter removed), after installing filter and cranking (cam rotating) for quite a while (to fill filter and pump to head), finally oil began to ooze up from that oiler hole in the head. It was some dark stuff at first, but clean oil eventually began to flow, albeit slowly, which I have read is typical.
If all that doesn't do it, Charlie's suggestion touches on one other possibility, leaking around that one cam journal supplying oil or perhaps the wrong cam bearings were used? I haven't had mine apart, so I am unfamiliar, but it's my impression that oil must flow into and around the cam to make the thru connection to the head?
