In addition to the ATSG manual, there is a GM training manual for the 200-4R. This 91 page manual has more of the theory of operations flavor for the 200-4R and is more detailed than the ATSG manual IMHO. As an engineer, I like to start with answering the 'why' questions before looking at the 'how'. I got mine off eBay, it was printed by GM in the 80's and I'm not sure it is available any longer from GM. It is a great tutorial on the 200-4R. Good Luck finding one tho...
No, the Principles of Operation book is out of print. Great book though; I love mine. Last time I tried to order some (couple years back now) Helm, I believe it was, was selling black and white reprints.
Kinda cheesy but better than nothing if you can get one of those.