There are a number of books about R. G. LeTourneau and the machines his company built. These two books are written, or being written by the author of this website.
R. G. LeTourneau’s Overland Trains: a complete history by Mark Moore. Available on Amazon in Kindle eBook or paperback, published September 2022
Untitled book on the LeTourneau Tournaplanes by Dale Hardy and Mark Moore, target publish date 2024.