There is great information about Don Stevens on Meher Baba's Life & Travels website. Don died in London on April 26th 2011, having being born in Nevada in 1919. It was interesting to hear him mention that after deciding to leave the oil industry, he considered training as a Jungian psychotherapist. Of course, Baba made it quite clear to Don that his involvement in the oil industry was needed to expiate his karmic dues and he did not want him to leave it.
Returning to that first book about Baba that I read, I came across Listen Humanity in a little bookstore in a small town (Nowra I think) south of Sydney. At the time, I was with my second wife Sylvia who shared in a number of serendipitous discoveries relating to Meher Baba. It must have been late 1993 or early 1994. It was Sylvia who found the book, bought it and wrote the date and a comment inside it. The physical book is in Jakarta, while I'm currently in Brisbane.