The photo of David Douglas Duncan shows him with a Nikon lens on a Leica screw-mount rangefinder body. If you search around on the web, there are interviews with him about it, for ex https://www.bandwmag.com/articles/david-douglas-duncan-the-making-of-a-master He says they modified the lenses to fit the body. Later (I'm guessing it was later), Nikon lenses in M39 screw-mount were a factory product. In 1950, the Nikon body available was a Nikon M, which is a collector's item now - with the odd 24x34mm frame size. I have only ever seen one under glass in a museum.
God Bless him.
He lived a long time