Hy svwilbur, lots of questions, if you will use the original oil fill tube in the front of your manifold shown in your picture [without the fill tube] you could buy a cap for it with a hose connection in it, you could hook your pcv system up to that. No need to reinvent the wheel and start drilling holes in your manifold. Incidentally of course cast iron can be drilled and tapped. The tin cover is there because exhaust gas is circulated under the carburetor, without the cover, oil would burn to the area and cause quite a carbon buildup in very short order, hope that helps.
