OK, where is a good resource for film holders? They are not too common on the ground where I am..... Even if I could get the dimensions for a common holder, I could at least still build the camera around that, but also build the MDF back for now.
Also, I don't have a 8x10 enlarger either (I can only go to 6x7cm), so the intention was to contact print. That was another question. How fuzzy would an image get contact printing paper on paper?