Ray Bradbury never worked on pictures with John Houston...

The writer was Peter Viertel, who was a screenwriter and novelist who worked with both John Houston and also Hemingway.
The story is based on John Houston and the shooting of the African Queen. The novel and movie "White Hunter Black Heart" is not really about African hunting things, but is an insider Hollywood movie making piece.
But John Houston was into hunting in Africa and actually did make the movie on location in the Congo just so he could do it. (There is a good photograph taken by Katherine Hepburn of Houston cleaning his guns, she captioned it: "John Houston, with his first love")

Peter Viertel also wrote another book called "Dangerous Friends" which was about his relationship with Houston and Hemingway.