Through 1958 they did have a 1/16" restrictor in the oil supply to the rockers which can plug up.
Up through 1957 it was the lower rear fitting the supply tube screwed into (under side cover).
1958 has it in the block right behind the plug where the old tube would have atached in the center of the block(under side cover).
1959 and up has a 11/32" restrictor in the same place as 1958 which is hard to plug.
