u/Final__Pie

I recently bought this Luger and it has almost matching serial numbers with the exception of the full serial number which appears to have been ground off. in addition, theres a weird spacer between the body and the barrel. There is one proof marking but I cant ID it, and the bottom of another on the body but the rest has been ground off. Can anyone shed some light on the markings as well as why it might’ve been ground and that barrel insert added?