anybody ever seen one of these before?

[DonVoigt]

Not exactly like it; but several/a few 'smiths have created .45 lugers in the past.
A fixed mag is about the only way you can get a .45 round into the grip of a "normal" luger frame.

Lugermans .45 lugers are copies of the "1907" US trials guns, and are larger than "normal" in all aspects, and use a removeable mag.

Werle has made many different luger creations, but does(usually/always) mark his.

Wyatt also made a .45 luger, but it loaded from the side of the grip. And could feed from a new made oversize magazine.
Others like Martz made their .45 lugers by cutting two frames, two receivers and joining them by welding to make a larger frame.

I think it is a one of US creation, using the grip frame "made in Germany" from an import from the 1920-30s. JMHO.

A couple of us on this forum have single shot .45 lugers.
Here is one I put together in .45 GAP, which I almost- but not quite got to feed from the frame with mods.