I've used the black foamcore to construct a square box with an internal septum running vertically from front to back. There is a pinhole located on either side of the septum in order to expose sequentially or simultaneously. This give me two vertically-oriented 3 1/2"x5" pictures on a single 5"x7" sheet of film. If exposed simultaneously, I have a stereo pinhole image set. I also took the 5x7 groundglass spring back from an old Seneca view camera I had with leaking bellows and taped it to the foam core box in order to allow easy use of standard sheet film holders.

Joe