Seeing as how a standard 8P (8 perforations) wide frame of 35mm film is 36 mm x 24 mm, and the Stereo Realist frames are 5P, this makes them roughly 22.5 mm x 24 mm, I'd say that half-frame mounts would work, though you'd lose a bit on each side. Note that often the frames overlap by a millimeter or so on film put through a Stereo Realist, but the half-frame mounts will cover this up just fine.
As far as scanning Stereo Realist images goes, I've got a Pacific Image PrimeFilm 7200 that I use to scan them with. The software that comes with it should be able to detect the frame edges for those mounted in slide mounts. I run color negative film through my Stereo Realist and have the lab return the negatives uncut. I then cut them in strips of 8 frames (8 5P frames is the same width as 5 8P frames) and pass them through the scanner twice (because the scanning trays have a bar that runs across the film every 36mm as it assumes standard (8P) frame size). On the first pass, I scan frame #s 1, 3, 6, and 8. I then take the tray out, scoot the film over 4P (so that the frames that didn't get scanned on the first pass don't have the bar running across them), and put it through again, this time scanning frames 2, 4, 5, and 7.
Scanning standard 35 mm (8P) negatives or slides, I can scan a roll of 36 exposures in about an hour. If I'm scanning 5P frames shot with the realist, it's closer to 4 hours, because 1) I'm scanning each strip of negatives twice, and 2) there are 29 stereo pairs on a 36 exposure roll of film (so 68 images).
If you're looking to scan Stereo Realist images for mono viewing, just scan one of each pair of images instead of scanning them both.
Hope this helps!
