If you are referring to the
oil passage that feeds
oil through the rocker stand to the rocker arm assembly, one of the
oil modifications that is done to the FE engine is to restrict the oil flow to the heads by reducing the size of that oil passage. This is done because the stock passage allows too much oil to the top of the heads and the valve covers begin to fill with oil. The oil return holes cannot keep up with the amount of oil coming into the heads.
Check the allen head screw closely to see if a small hole has been drilled into it to allow some oil through. Some people thread in a card jet. This restricts the oil but lets enough through to lube the rockers.
Do a search on this forum " oil mods". This will explain in more detail
Paul