Strange holes in 240/340 manifolds

I"ve discovered a curious situation that"s got me stumped. I purchased a used manifold on eBay for my 340U, to replace the existing one that is badly pitted. After cleaning the "new" one, I just discovered what looks like two 1/8 inch holes, one in each passageway leading to the square shaped central exhaust ports on the underside of the manifold, behind where the carburetor bolts on. They almost seem like they could be water drain holes becacause they are right below where the exhaust pipe threads in. They don"t look like they rusted thru on their own because the metal is pretty thick and the edges are sharp. Was this a common thing to do to provide water drain holes?

Well, I happen to have the manifold off on my 240, which is identical to the 340, and in exactly the same two locations there are two welded or brazed plugs of some sort that appear to have been added to plug two similar holes. Has anyone else encountered anything like this? I"m wondering what to do, as I obviously don"t want an exhaust leak. I don"t want to weld them because I just had the manifold powder coated. I"m thinking I could drill them out with the appropriate tap drill, and thread the cast iron for a couple small machine bolts. Or would some sort of JB Weld seal them up?

Those holes are supposed to be there. Their purpose is to drain any rain water that might get in before that water can get into the engine. Pretty nifty idea really, but most of them are plugged up with exhaust carbon and rust.

Thanks! I didn"t know that. I"m particularly glad to hear it because that"s one less thing I have to fix!!