The Crown N proof dates it to before the general use of Nazi eagle stamps in 1939. I have a 1911 catalog showing Mauser and FN single shots of the same general configuration but not JGA.
The "Made in Germany" and ".22 Long Rifle" indicate it was made for export to the US or other English speaking country.
It is old, was inexpensive, and is well used. I think finding an Anschutz front blade sight is pretty hopeless and not much worthwhile. I would trot right down to the gunsmith and have him put on a Marbles front sight of the correct height and call it good.