In reply to the query about tracker bar hole sizes from Tom Griffiths
(MMD 11/10/1998):-

31 note rolls are cut with 3mm diameter holes on a 4mm pitch. From my
experience with keyless organs, the tracker bar holes appear to be
drilled the same size or up about 0.5mm diameter smaller than the holes
in the music.

I am sure someone out there in MMD-Land can give a much better answer
though.

Good luck in building your organ.

Jeremy Brice.
Watford, Hertfordshire, U.K.