Who else could have played McMurphy in 1975?

I was thinking maybe Steve McQueen, or maybe Clint Eastwood, but I think both of them would have been far too cool to play the ranting, raving McMurphy. McMurphy is a tough guy, certainly, but there's something about him that suggests he's a loudmouthed asshole who wasn't taken very seriously outside the mental hospital. I don't think Eastwood or McQueen could have pulled that off. James Coburn, while mainly known for cool, serious roles, played a few characters who were more bark than bite, but by 1975 he might have looked too old for the role. Lee Marvin as well.

Maybe Gene Hackman or James Caan?