I doubt you get much shift movement out of that arrangement due to the body flange to sensor cave. ;- ) right ? Also, 35 isn't very wide IMO so the GFX + any view camera type lens is useless for any wide angle shooting, especially if needing shift.
What I would want ideally is 4x5 coverage, or at least 6x12, from a lens not needing a bunch of post BS to make it work. I'd want to turn a 33x44 digital back into portrait, then overlap stitch for a 1:2 proportion which is only about 44x88 but in reality the lens needs to have a larger image circle for quality in the capture zone. Even then, the 30mm GF TS lens can almost do that right on it's own LCC issue-free body.
I'm probably just mentally stuck wanting a digital version of what used to be the gold standard. I don't have a drum scanner as I missed that window of opportunity when they were dumped by all the pro labs but I do have the Nikon "Super Coolscan 9000 ED" which is about the next best thing for 120 film.
With GFX cameras, the sensor is in a fairly deep cavity. This limits shift to around 25mm before hard vignetting. I have one lens that can go a bit farther. Wide angle symmetrical lenses will be max 25mm. If you are flat stitching, you can get around this because the stitching software will ignore the vignette area if there's image data in the overlapping file.
The widest symmetrical lens that I can use on my F-Universalis + GFX is the S-K APO-Digitar 35/5.6, and it is limited to 7.5mm of shift. This is why people who want wider angles with lots of shift use technical cameras and Rodenstock HR lenses. If you need wider on GFX, it makes the most sense to use the 24mm Canon T-S lens, despite it being less than ideal.
For your specific challenge (stitch for a 1:2 proportion to produce the equivalent of a sensor that is 44mm x 88mm) you need to be able to shift 28mm on the short axis. That requires an image circle of 99mm, but you're right at the edges so your quality expectations will not be met. Ideally you're after a larger image circle. You could pull this off with a lens designed to cover 6x9 film, but it won't be a wide lens. For instance, the APO-Symmar 100/5.6 I use could handle this because it has a large and good circle of good definition. On GFX, you will have to deal with mechanical vignetting, but as I said earlier it's a solvable problem if you shoot the required three images (shift, centre, shift).
A final issue you have to deal with is whether you have enough shift room on your camera. My F-Universalis only shifts 25mm left and right. I can do more by shoving the standards in their holders, but that's a pain.
The elephant in the room is do you really need that many pixels? How large are you planning to print these files? Using a GFX 100 series camera, the 44mm x 88mm "sensor" is producing a file that will print 78" on the long side at 300 ppi.
