I picked up this Tru-Vue stereo image viewer at a photography swap meet event. It was dirt cheap. It's for image pairs laid-out in a rectangular format, where you slide a card up and down to see different images in a sequence.
My thought is that I can print up Sputnik image pairs on transparency paper, in the right layout to work with this viewer. It might also come in handy for looking at "proofs" of viewmaster shots, somehow. A quick scan and print, and it'd be much easier to "preview" my shots without having to actually punch 'em out and stuff 'em into a real reel.