Need help with 1916/1920 DWM Circle-S stamped Luger

A friend is hoping to sell me an interesting 1916 DWM Luger -- or at least the upper is a DWM. It has the mysterious Circle-S stamp and a 1920 stamp as well. In addition, it appears to have a Nazi proof along with the WWI Imperial proofs. The upper and lower halves don't match. And it sounds as though the magazine is a WWII-period aluminum-base one. It has no extra magazine, tool or holster with it.

I don't think the pistol has other rebuild or police markings; nor does it have a sear safety, if I remember correctly. I haven't seen the Luger in years, but he did send me some photos, which I am including below. The photos aren't the greatest but are all I have at the moment.

With the mismatching it has, I'm wondering what a fair offer to him from me would be for it. Also, any ideas on how the mismatch came about? Field repair? Bubba? I suppose it's hard to know. Thanks in advance for any replies....

Well it s DWM receiver and toggle. A Mauser barrel and who knows who made the frame. So a real mismatch. I think that it may be a parts gun.

In the UK (a much smaller market) I reckon that most of the people who want a Luger have one, the dealers are awash with guns, and those that are still looking for a Luger will only buy the best. So a mismatch like that will struggle to make any kind of money in the UK.

Personally I would not buy it