Death Head Luger Question

Hello, Yes I am a newbee. But I have done alot of reading on this message board, and I like it. I have come across a Death Head Luger (1916 DWM) on a Mauser lower frame (toggle pin retaining buldge). How do I know that the, atleat the upper part is real or fake? Is there any way to tell by the Death Head stamping? I really feel that it is not authentic. But you never know. I am also sure it is a East German Rework. Any Thoughts?