Audii-Dudii
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This is just a crude, outside-the-box, prototype to test whether the image quality that can be achieved will justify the effort of adapting the lens properly, but it definitely works -- ! -- and the initial results are promising (IMO, anyway ... YMMV!):
The lens is the legendary Zeiss 38/f4.5 Biogon. It's the same lens Hasselblad used for its early SWC cameras, except in this case, it was salvaged from an AGI F135 aerial reconnaissance camera. The camera used a pair of them to cover 70 mm roll film, along with a large, electronic control box that operated the electronic shutter and aperture mechanisms.
Unfortunately, because the F135 was an aerial camera, there is no focus mechanism since it was locked at infinity and adjusted using shims. For now, I have tweaked the FFD to set the lens at roughly its hyperfocal distance and in the event I decide to continue with this project, I have a few ideas about how to add a simple focus mechanism without significantly modifying the lens. (Note: The rear element extends nearly 8 mm into the GFX 100S and just clears the body's electronic contacts. The diameter of the rear element is small enough compared to the GFX lens mount that, in theory, it can be shifted up, down, or sideways by roughly 5 mm, so it may be possible to use this as a shift lens provided I can design / fabricate the appropriate mechanism ... we'll see, but if I can pull this off, it sure will be a hoot, eh?)
FYI, I've had this lens since 2002, when I purchased it for $200 to use with my Toyo 23G medium-format view camera. In this application, its short FFD -- 28.7 mm -- and lack of a focus mechanism weren't significant issues, because I focused the lens by moving the rear standard along the camera's central rail and when used with Toyo's deeply recessed lens board, I could just barely focus it at infinity. The lack of a working shutter (as there is no way to use it in its original form in the field) wasn't an issue, either, because I always shot at long exposures, thus simply counted off the time and used the lens cap over the lens to start and stop the exposure.
But enough of that, you say, how does it perform? Well, based on this test photo taken yesterday afternoon standing outside my front door, its prospects are promising, especially if you're a fan of the traditional Zeiss rendering style, which I very much am:
And with the XPan, 65:24 crop, which is how I initially plan to use it, assuming everything proceeds smoothly from here:
Because the lens was designed to cover the 6x6 format, its image circle is between 82-84 mm in diameter, depending upon where you draw the line on sharpness in the corners. Due to the nature of its design, its circle of illumination is subject to the COS^4 law, so it does gradually dim toward the outer edge of the image, although not (IMO) objectionably so...
Anyway, I thought I'd share this for grins-and-giggles... 
P.S.: There is a similar version of this lens as used in a different aerial camera available on eBay for $1,700! Of course, it's been listed there for more than four years, so I suspect the seller's price is a bit above the market rate for them (not that there are many of them available, mind you.)
Noon-ish Update: Miss Abby and I went for a walk this morning and I brought the camera along, taking these two photos (as well as many others) along the way:
A few observations: 1) The lens isnt happy when it's pointed directly toward the sun (I added a clamp-on hood for some Minolta MD lens I had on hand, which definitely helped); 2) As presently setup, anything in the foreground that's closer than, say, 20 feet won't be rendered razor-sharp; 3) Even with the XPan format crop, there is a bit of smearing / softening in the very tips of the corners and along the side edges; and 4) It's fun to be working with a fixed-focus, point-and-shoot camera having a 102 MP sensor ... lol.
All in all, though, I generally like what I'm seeing! It's obviously not a modern-design lens and its performance is far from perfect, but I'm after a visually pleasant character, not absolute perfection, so that's plenty okay by me! 
Yet another update: I did some aperture testing this afternoon and discovered I had set the aperture around f6.3, which is roughly two stops less than I thought. As you might expect, stopping down to f8 and/or f11 has noticeably improved the image quality, as well as increased the apparent DoF ... win-win!
And here's a photo I took late this afternoon while taking another walk with Miss Abby:
I have to admit that using this camera-lens combo as a glorified point-and-shoot camera is a lot of fun!
Project Permanent Mount is underway!
I opened the lens and removed the remains of the not-needed electronic shutter assembly (although I had to leave several parts of it in place to serve as shims and/or spacers.)
I also confirmed there's no easy or accurate way to remove any of the excess metal from the housing without using a lathe (which I don't have or have access to), so I won't be able to reduce the weight or size of the lens (at least not at the moment.)
The other reason for splitting the lens in half is that it's a lot easier to transfer the screw hole pattern by using the existing part as a template than it is to recreate it by measuring the spacing between the mounting holes ... btdt many, many times in the past.
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