I find it easier to imagine him as Jamie. But actually I think King often doesn't describe what his characters look like that precisely. He describes their clothing and their demeanor, and what kind of impression they make on people, but not so much else. He gives details sporadically, he doesn't go by every feature like hair, eyes, nose, mouth, length, if they're thin or heavy etc. He will mention details mostly when there is something special about it, like after Jacobs had a stroke, one half of his mouth wouldn't work anymore.I can see Crowe as the preacher. Maybe he will play Jacobs.
Some writers completely describe every feature when a character is first introduced. But I think mostly he doesn't do that, so you imagine them more yourself.