Most period photos would be hard to tell. I don't think I have ever seen one with both top and bottom lugs being captured by the adaptor. Also the lack of a hinge on one side is not normal. I am guessing it has no proofs? So I am guessing either a locally made item early war or a collector made item. Why is it in the white? Is it painted or blasted or... so its not possible to really see the age by the condition? How about a close up on the wingnuts and all thread. That should be telling.
Some closeup pics of the construction of the adaptor would be vety helpful. Especially the bayonet fitting at the bottom. Are the top and bottom pieces welded on? TIG, arc or how are they done? Looks very contemporary to me and not at all 'vintage'.