What a great idea dyi stereoscopic camera... Im gonna have to give that some thought. The obvious camera of choice would be the 116 as a start. The negative area is 2.5 x 4.25 if i'm not mistaken. They are also reasonably easy to come by. I have adapted them to a medium format panorama. So you could easily adapt one to use two smaller lenses or even pinhole apertures. Yes that's the ticket... a pin hole stereo camera on a 116 frame.
A couple of tomato paste cans for lens barrels and you are over. Not sure about how you would make a viewer for it but that idea would work. I like it, now if i can convince my wife to have spaghetti next week. Im dead serious that would work...