This does -not- directly address the actual question you asked, but....
Have you considered the "Lazy Man's Solution(tm)" to the basic problem? To wit: 1) "standard design" bookcases 2) some 1x2 stock, in various lengths
Where you want to have books 'face out', you simply lay down (loose!) a strip of appropriate length along the back of the shelf. Then stack the books in, bottom of the book against the 'spacer', top of the book against the back of the case. Voila! Books lean back, so they won't 'jump off the shelf'.
Do the dimensions right, and you can use the _same_ spacer for full-size hardbounds and paperbacks, simply by rotating the stick,
Note: the 'spacer' doesn't even have to be wood -- a piece of cardboard, folded into a triangular tube also does the job. And you've got a continuing source of _that_ in the cartons books are sent to you in. Hard to argue about 'free' materials.