I recently found this eBook on the Internet Archive and, based on the portions I’ve read, found it to be a very extensive and detailed account of the James and Younger gang and the Younger brothers. It was written in 1882 while the memory of these bandits and killers were still fresh on the minds of the American population. This band of outlaws ran roughshod over Missouri, Kentucky, Iowa, Texas, Arkansas, Kansas, and West Virginia.
Certainly bank and train robberies are big payoff jobs for any outlaw gang. Portions of this book can be used almost as how-to templates for gaming purposes. The author gets into the details of many of the robberies and hold-ups committed by these “daring outlaws”. He also provides information on the efforts of the Pinkerton agents and other lawmen to bring the gang to justice.
I cleaned up the Google Book version of this book and the link is below. (I just put this one on my tablet today and it looks good and is easy to read.)