That line goes all the way through the water jacket and comes out under the side cover near the center of the engine. It's the oil supply for the rocker arms. Once it's installed, those compression fittings are not serviceable- - - -the line must be destroyed to remove it, and a new one is installed. Some of the antique parts vendors sell a kit with all the bits and pieces to do the replacement. Be sure and drain the coolant before you start the project, and you'll only get one shot at getting all the bends right on both ends!
Jerry
