Agree with posters explaining that one rocker shaft bolt on each side goes into the oil feed hole that comes up through the head. Some rocker shaft pillars have wide inside diameter holes and the oil will easily come up around the threads and into the shaft. Some though, have a narrow ID and must take a thin shank bolt to let the oil by. So pull your bolts and check them out and find which one will work in that oiling pillar.

And yes stick a wire into the oil hole through the head and make sure it is not clogged up.

Also I read somewhere the rocker shafts have a "front" and a "rear" but I don't remember enough to explain it.

puttster