Help!! Please identify this long barrel luger

[markbritt]

I hope I am placing this post in the correct forum, as a collected indicated to me that this is a military luger, not commercial. I recently acquired a long barrel luger. All the numbers match except for the hold open latch and the firing pin. German or Made in Germany is NOT present on the barrel or frame.
I purchased it under the idea that the long barrel was a custom add-on. After purchase, I cleaned it up and see three interesting things on this barrel. First, the sight base is the correct height for a German production barrel, second is the proof stamp found on the front of the sight base and lastly, there is a witness mark on the barrel right next to the frame. I took some pictures here and a closeup of the slide serial number. From what I can tell, the 2's look like a double strike, not an overstrike of some other numbers. Could anyone tell me what the proof on the sight ramp means? Is this an all German gun? Is the double stamp of the slide serial number original? If so, what would an estimated value be? Any help would be appreciated.
Thanks in Advance,
Mark