The rocker arms only need a small volume of oil to lubricate them, but it MUST be there. The restrictors are there to prevent robbing the lower end of the engine of the necessary oil flow- - - - -if necessary, sacrificing the rockers to assure enough lubrication to the bottom end. That's a throwback to the "oil distributor" on the old spray-oiler engines, 216, early 235, etc. that restricted oil flow to the head until there was at least 15 PSI at the main bearings and oil spray tubes in the oil pan. From 1953 with the first full pressure 235s to the last of the series in 1963, there were several variations of the rocker lubricating system.
Jerry
