More on the table, I spotted on a forum about alternate history, a discussion forum who talk about the numerous "what if?" in History, some threads about what if James Dean lived longer?
http://www.alternatehistory.com/discussion/showthread.php?t=107407
http://www.alternatehistory.com/discussion/showthread.php?t=276300

I spotted also to clip of a screen test of James Dean with Paul Newman and speaking of Paul Newman, I spotted that info on IMDB
"The role of Rocky Graziano in Somebody Up There Likes Me (1956) was originally awarded to James Dean, who died before filming began. Due to Dean's death, Newman was cast in the role. Dean also was signed to play Billy the Kid in The Left Handed Gun (1958), but that role was also inherited by Newman after Dean's death. Dean and Newman had shot their last screen tests for East of Eden (1955) together; the six-years-younger Dean got the part and Newman went on to star in The Silver Chalice (1954), a notorious turkey."



Come to think of it, if James Dean had lived longer. I wonder if Sergio Leone could had chosen James Dean instead of Clint Eastwood for the role of "The man with no name" in Leone's westerns?