Have you seen https://www.ibmmainframer.com/ https://www.ibmmainframer.com/? I would also dig through Project Guttenburg https://www.gutenberg.org/ https://www

Have you seen https://www.ibmmainframer.com/ https://www.ibmmainframer.com/? I would also dig through Project Guttenburg https://www.gutenberg.org/ https://www.gutenberg.org/ for IBM Mainframe Programming books if you're interested in the history.