You've got me thinking about Mitchum and what a wonderful actor he was. I was reading round and found the quote- from an interview with Barry Norman- where he says (I'm paraphrasing) "I've got two acting styles- on a horse and off a horse".
In fact he had considerable range. The psycho in Night of the Hunter and the mild-mannered school teacher in Ryan's Daughter are worlds apart- and yet he infuses both with essence of Mitchum.