There's a couple of times the Eastwood/Roland comparison is explictly made in the books. Eddie makes the comparision when he and Roland first meet face to face, I think.
A DT movie would be bad. BUT a series/mini-series on HBO or something could get it done, I think, especially given how the series ends:
Spoiler from book 7:
The last episode could end with the beginning of the first episode, except that Roland wears the Horn.