I think I do not want to risk getting metal in an oil journal, if I tap that hole. I think I am going to first try a brass plug.
I will take Deve's advice and clean the hole to be sure it is not threaded. We slid a small screwdriver on the edge of the opening/hole - it seems to be smooth. I'll try to take a photo that gives a decent depiction of the hole.
There is no question about the hole being a smaller diameter - as if it had not been tapped/threaded.
