I didn't want to throw that spoiler out there. . . but ya, I kept saying to myself "No way it's an alter ego. He's already written that story." Over all, it was different from The Dark Half, but at the same time, same idea. Wonder if halfway through The Dark Half, he thought of this angle for the story, and just waited to put it down on paper, or something.
And, do you mean The Shinning? He did go there to write a novel. However, not sure if "All work and no play makes Jack a dull boy." counts as a novel.
King has a lot of stories/books with writers as main characters. A lot of writers do. And, of course, some of these were written back when King was a druggie/alkie so it was as if he had a built-in alter ego.
