There should be no external line going to the valvetrain. The line on the drivers side should go to the oil filter (if equipped) and have a line that goes to the pressure guage (using a T if used with a filter). The only line to the rockers will be on the passenger side, behind the lifter cover on models up to '58, after which they use a drilled passage in the block.
If you have an external line, then it would seem that somewhere along the line a po has done a backyard repair to fix a blocked passage/oil line.
