Thanks for the reply. Have you considered making a shorter box (can you shorten an Eddystone box?) with a large, e.g., Compound #3 or larger or Ilex #4 or larger, leaf shutter in front of it with a PX 67 female mount attached to the shutter?
The obvious step beyond that, given my prejudices, would be to change the rear (stepped plate?) to hold a Mamiya Press "M Frame" (better in some ways, perhaps worse in others) or a 2x3 Graflok (worse in some ways, perhaps better in others) and to use, respectively, an S-shaped Mamiya Press roll holder or a Graflex roll holder. Mamiya Press roll holders are supposed to hold the film flatter than Graflex ones but I don't know where Mamiya ever offered a focusing panel for the M Frame. With a Graflok you'll have a focusing panel, will be able to compose through the lens.
A question. Why carry several inserts for your roll holder? They're not light tight, can't be carried safely loaded, and have to be in the shell before film can safely be advanced. Using an RH-8 insert in an RH-10 shell wastes film. If you can take an insert out, you can reload it and put it back in.
I have a little experience with a broad range of lenses (45/9 WA Dagor to 480/9 Apo-Nikkor) mounted in front of a Compur/Copal #1 shutter on 2x3 Graphics, have had no difficulties with vignetting and few difficulties, including one huge embarrassment, with loss of diaphragm control. Diaphragm control can be lost when the shutter's maximum aperture is smaller than the lens' exit pupil.
To be clear, I'm far from sure that a #1 won't give you vignetting because I don't know how far your lenses' exit pupils will be in front of the shutter. It works for me because my front-mounted lenses are always close to the shutter and the shutter is usually relatively far from the film plane. Not your situation, in general.
Good luck, keep on having fun,