[Synchro909]

Weeping along the left side of the engine is almost expected on a Model A engine so I wouldn't get excited about it. As for loosening a nut, I once had the thread in the block strip on me when I was retorquing the nuts on a newly rebuilt engine. It was one of the two that hold the water outlet as well. I knew the thread was not very good but I also knew I could fix it later if it let go. When it went, I drove the car 25 miles with that stud in my pocket to a friend's place to install a Helicoil and the head gasket was fine (still is).
In your case, if you are concerned, I suggest draining the coolant to below the head and go for your life.
BTW, Why are you opting to do things that way? There would be no drilling into the head if you were to put a short length of metal tube in the top radiator hose for your source of warm water and return it to the one running from the bottom of the radiator to the engine. A thermostat fitted above the attachment in the top hose would help the flow.