I second the oil galley plug theory. There are actually three. Two in the front behind the timing cover. If one or both, or all three are missing, you won't get oil to the rockers. The two behind the timing cover are just drive fit and staked in. The third one you are able to see if you remove the distributor and use a small mirrior in the hole. It is a threaded plug. If it's not there the motor's got to come out. Access if through a freeze plug in the rear of the block.
