I've been under the weather for a few weeks but I've been following the threads on my iPhone. I have a bellows drawn in my Cad program and have made one in the past. For that one I used XRay film for the ribs and it turned out to be a little thicker than necessary. I used fabric at the time from the fabric shop and 77n spray adhesive and contact cement. I'm lucky to have purchased two large pieces of the bellow material that Porter's camera had before they quit selling it. Too bad because many would appreciate having a supply in the west.
My camera is using the base of a Kodak 2D but built from there up. With film holders going for $345 new I'm forced by choice to go with my own build on them too. If I go at it I'm not going to be happy with one or two holders. That would be fine for a home setting but why drive out to a location and be forced to load in a tent or do without.
I was thinking that the double sided holders was the way to go but what's the matter with single sided holders. A dozen would be about right. I was thinking about what you said about alternative holder designs. I am thinking of ordering some 10X12 film from the Ilford special order. A 10X12 would fit on an 11x14 sheet of paper for Carbon Transfer which needs a safe edge.
The wood workers store has some really strong magnets, small but very strong, they sell them in sets as catches for cabinets. I was going to try a setup with them to see if they have the holding power. In the mean time I've worked out the routine, regular holder design. I may be short on metal working machinery but I'm long on woodworking tools.
I have an older but new like Sterling holder, the double glass type, and measured the slides, Garolite, and figured the configuration by dissembling an older 5x7 holder. It's precision woodworking but not rocket science.
Your camera is looking excellent, I used brass for the hardware on mine to match the original parts but on a future 11x14 model desgin like yours I'm thinking of aluminum with a powder coat. It's lighter than brass. I can't wait to get back to work on mine. It does take time to get these together.
I'm making a spring back because I have the ground glass and springs for an 11x14 already here.