At first I didn't know the lens was removable but a bit of Googling told me more about the Diax IIb. The camera body was in very bad shape, but thankfully the lens is great condition. After removing the lens from the camera, I mounted the lens the same way I did with the Retina-Xenon; with a 52mm filter ring at the rear, and then attached to the Yeenon 18-33mm focus helicoid.
Diax IIb with lens detached. Click for larger.
Brothers: Retina-Xenon on the left, Diax IIb Xenon on right - Click for larger.
I briefly tested the Diax IIb Xenon 50mm f2 this afternoon, and I am overjoyed. This version of the lens is even slightly better than the Kodak Retina version. At f2, the lens is sharp corner to corner, with just a bit of loss of contrast. One stop down, it's excellent. As expected, there is just a bit of vignetting wide open but not worse than modern lenses. A nice bonus, the lens comes with a 14-blade (could be 13, couldn't count) aperture, whereas the Retina version has only 5 blades.
Like the Retina version, this lens renders bokeh with such silky and exquisite smoothness that I am quite enamored of. This could become one of my favourite lenses.
All pictures below were shot with the Sony A7 and the Schneider-Kreuznach Xenon 50mm f2 lens from the Diax IIb, at f2.