Jesus Christ, Bill Haley is one uncool guy. While Elvis is no longer controversial at all, he still comes off as cool when you see old footage of him. Bill Haley, on the other hand, comes off like a lame middle-age white dude who finds Elvis to be "totally crazy".
Also: the age difference with love interests back in the day is kind of creepy. Why can't you just cast a dude who's not twice as old as his female counterpart?