These were 35mm stereo slide mount made of metal and glass. Very high end. We looked at taking them appear to scan and clean. The top and bottom of the mount each have two holes where the inside of the mount pushes a bump through. We looked at prying the inside and outside of the mount but found there is VERY little space to pry. Also, there a warnings about glass mounts that the film may be stuck top the glass and this may cause a problem....either the image gets damaged or you may need to soak the glass and image in distilled water (must have NO minerals otherwise more issues). Here's an image of the mount:

http://www.digitalstereoscopy.com/kaiser/m214n215.htm

Here's instructions and image of putting these mounts together:

http://www.digitalstereoscopy.com/kaiser/m248n249.htm