I own a book which might be useful. It's a memoir about an anthropologist living among the Songhay of ***** and eventually apprenticing himself to a local witch-doctor. Unfortunately, it's distinctly modern, being set about 40-ish years ago, I think. I'm presently away from my books, but I can get it tomorrow if you want to ask me some questions.
If you want to look for it yourself, it's titled
In Sorcery's Shadow.
You might also want to look into an RPG called
Spears of the Dawn. Someone did a chapter-by-chapter write-up about it
here.