Hello Robert,
Philip Balcomb has about a 20 page chapter on Cuckoo Clocks in one of his books, "The Clock Repair First Reader". The last four pages of that chapter focus on three train musical cuckoo clocks. It's basic, but very good information. Unfortunately, it doesn't currently appear to be available except at ridiculously high prices. Maybe you can find a copy with a little more digging.
The 90+ page book titled "The Cuckoo Clock Repair Manual" by William j. Bilger also goes into some detail on both Music Box Operation and Adjustment as well as Animation Automata & Revolving Platforms". It is currently available.
Personally, I find Mr. Balcomb to be a little easier to understand and follow but they both go into good detail with plenty of photos, drawings and diagrams.
I've only worked on one 3-Train Cuckoo and I eventually had to replace the Music Box because the original one had such a worn out Governor and Warning mechanism that no matter what I did, I could never get it to go into warning without sending the little Accordion Player out to play a few notes before waiting his turn to play. Installing and adjusting a new musical movement was such a breeze by comparison that I wish I had just decided to do so from the very beginning.
Good luck,
Bruce
