Please help identify my Luger

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Guys...thanks for the warm welcome and all of the useful information. Now that it's been mentioned, it does appear that the stamp on the underside of the barrel references "CDI". I really love the gun...its look and feel, even given the fact that it's a mis-match. I'll be less reluctant to take it out to shoot, afterall! What parts would have been replaced? All of the numbered parts (i.e., 2577) match. If the front toggle link is not original, does that imply that the "77" stamp is fake? Did these guns end-up as Russian Capture's because they were previously damaged or were they truly taken during the war? Here are the photos of the top of the gun. I welcome any additional comments.
Thanks, again.