Well, the easiest way to do this is to modify an existing 120 camera, either a folder or, as I did, a camera with a lens that pops out on a tube. If the shutter is still working, all you do is replace the lens with your pinhole medium, sheet brass or the like. The aperture is approximately the aperture of the lens you replaced, i.e. 75/80mm for 6x6 or 105 for 6x9. If you take your time, use the correct methods for making your pinhole, you will be amazed at th clarity of the images you get out of this type of camera. The spacing is done through existing red panl holes on the back of the caamera.
tim in san jose