I have seen this - you can crop the photos but this forum software will resize them for you.
I just saw your pictures - what number is on the barrel, underneath?
I would guess, one of four possibilities
1. Re-issue by east germany
2. possible, but doubtful that the upper slide was replaced at a depot or armory
3. post WW1 replacement for sale to the public, this was done by many private firms
4. done post war by bob the gunsmith
Ed