When I asked for pictures of the "top" I wanted to see if there were anything stamped above the chamber". The shot of the "back" was to see if there is a stock lug on it and if it has a grip safety or not. From what I can see, you got a nice shooter there! With the numbers being mismatched and defaced, it has lost any "collector" value that might have had. I won't give you a value on it, because frankly, I don't know", BUT, they ain't making any more of them.
What I can tell you is that the toggle was made by Mauser-Werke (Code 42), but since it has a different serial number stamped on it, who knows where the rest of the gun came from. The toggle also has the German Military Proof mark on the side, If there is anything is above the chamber, that might help.
The crown over "N" is a German Commercial Proof mark. The eagle over number (seen on magazine) is a German Military Proof
The gun appears to have been military sometime in its life. The area on the front right side of the frame looks like it at one time had military proofs on it and looks as if it has been defaced.
This information is from "The Luger Handbook" by Aarron Davis copyright 1997.
There are some markings on it that I cannot identify and cannot find any information on.