I just ran across one of these in Granada mississippi. Same look, same lettering, same condition. I saw on your first post where someone said that the author of anvils in america hadn't ever run across any, so I feel free to make some assumptions.
I'm going to assume that they came without a top plate. Theres no way that both of these had the top plate fully separate if they came with one. I'm gunna assume they are cast iron based on the shape of yours and the edges of the one I found, and also it provides almost no rebound with a ball bearing test. So probably a flat, cast ASO, but still rare and interesting!
