Robert Leber enquires about the fold-to-fold dimension for book music.
This dimension really isn't too important, unless you have a particular
organ with a rather circuitous route for the music, or a restricted
music shelf on the back of a traditionally designed street organ.  The
page length is usually left up to the noteur, as he will have his own
jigs designed for his own size of book page.

The majority of organs appear to use a page length of 160 or 170 mm.
I have seen books with pages as long as 200 mm, but this is too long
for some keyframe arrangements.  If you are unsure, then simply copy
the page length on an original book.

If your organ is modelled on the traditional 'Carl Frei' street organ
-- with the music shelf positioned across, and within, the back of the
main organ case, where the music is placed at an angle to allow it to
unfold into the keyframe -- then go for 160 mm.

With best regards from GB,
Nicholas Simons