Supposedly there is a little brass oil pressure reducer (orifice) that goes between the head and the block and mounts in the block. I am certainly no expert, but I would think that if that was missing, you'd have excessive amount of oil going to the top the cam/valve cover area and be causing what you see. I did rebuilt my motor a couple months ago, but due to a block issue, ended up installing a JDM myself for cheap.
just my 2 cents