I made this thing years ago and haven't used it in a long time, so I'd like to give it away to someone who will.
It has a standard design for this kind of thing: a self-centering cradle for the book, a glass platen made of two sheets of glass at 90 degrees to push down on the pages of the book, and two 1/4"/20 thread posts to mount cameras. I used point and shoot cameras when I originally made this thing, but a phone (or two) would probably work better at this point. The platen moves up and down on a cabinet slider.