For the most part, those who spell their name "Crain" tend to have Irish, Scottish, or Isle of Man bloodlines. Those who spell their name "Crane" tend to be English.
Of course, there are exceptions to the rule. Some Cranes changed their spelling to "Crain" just so they wouldn't be confused with all their "Crane" cousins and neighbors (as in Connecticut and New Jersey). It's doubtful your James Crain is of the same family as Randolph Scott but the only way to make sure is to completely fill out the genealogies of every Crane in the U.S. And, trust me, that's not an easy thing to do. :D