I got this Idea in my head a while ago to make a Polaroid pack film back for my Graflex SLR.
After some measurements I found that The back from an old Vivitar slide printer and a piece of Masonite would work to get the focal plane right. I routed out a slot on the face so that a thin piece of plastic could act as a darkslide. With some velvet and epoxy glue to make light seals I was able to simply screw it on. Two thin strips of masonite glued on the edges lock the holder in on the same plane as the bag mag. After some sanding and filing of the metal spring to provide clearance it fit perfectly and works well.
I've taken one exposure on Fuji 3000 and It it in focus and with some pencil marks on the ground glass the subject is framed well.