Nice finds guys! I'd Love to find one of these in decent condition!
On the replacement of the "tires" - on a band saw I've simply contact cemented a strip of rubber onto the wheel. However, those run much slower and the Dia of the wheel is much larger... less likely to have issues peeling the "tire" off. (Minelasted for 20+ years, and was still working fine when I sold the saw...)
For a roller like these I think the bicycle inner tub is a good idea, however, see if you can find what they used to call "thorn proof" tubes, as those are thicker. Use a large Diameter tube (not the 20" ones) so as to reduce the curvature.
If a Bike tube isn't a decent option, you might do the rubber strip, and wind it on slightly diagonal (overlapping the edge of the roller) and trim to width when done. this would I think give the least likelihood of stripping the rubber off at speed.
Motors: If you want variable speed, a tread mill motor could be easily adapted to one of these, however I would set up the pulley sizes so it's not likely to "over rev" the sander rollers/belts at speed. These things can go 4-6K RPM's full tilt...
