Hello Sean
The Allied and Axis monographs had at least one issue with Diamond T coverage. There is also a back issue of 'Wheels and Tracks' with coverage.
There is also a couple of books published in the UK about the 40-ton transporter, there's one here
http://www.hankstruckpictures.com/nynehead_dt_book.html
Plus Warehouse Publications produced one, but their website is down currently.
Hope this helps
Steve
PS Which kit did you buy?