I would have to agree that it is some kind of customized Lyman sight. But I must also say that it is very well done. It looks like it came from the factory so maybe Lyman actually made them. Another interesting thing is that there isn't any exposed screw to hold it on to the rifle tang. The screw must come up from under the top tang and you have to remove the butt stock to get at the screw. I'll take some close ups of it and post when I have a chance.