I think that Roland's father should be played by Clint; it's the kind of full-circle thing that Steve King loves. I also think that the perfect person for Eddie Dean would be Colin Farrel (can't you just see that "you can't be serious" look that he does being given to Roland?)... he has the perfect Eddie-tude.
Wasn't Cort fat, though? Or was that just the comic (or even bad memory )?
I like the idea of Clint playing Roland's da'. For Eddie Dean, however, I'm privy to the idea of Aaron Paul, and he even wants the role. It'd more or less be a similar role to his role in Breaking Bad.
Clint Eastwood is 187 years old now, sadly, and not particularly right for any of the roles. Which is why someone needs to invent a time machine and just go back and snatch him out of 1978 or so and have him come back here and play Roland.
Otherwise, he needs to not be involved in an in-front-of-the-camera capacity. Except maybe as Callahan. That'd be cool, I guess, although he's a good two decades too old even for that role.