The 68 is a funny code the maker used. They would stamp the last 2 digits of the serial number on the outside of the sideplate, then stamp the first 2 digits PLUS 1 on the inside. They only did that for certain years, and I'm not sure that it was always done during those years.
Try to get us some better pictures, because that first photo makes me think you have a good original Luger.
dju
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