Yep, I have read The New World Order. Good book. Well documented.
The Unseen Hand is another good book by Ralph Epperson. I even know Ralph. We've spoken on the phone several times. He's a gentleman. His book is well-documented and he backs up everything he says.
No, I don't think Stephen King was referring to Ralph in 11/22/63. Fantastic novel with a captivating plot and great characterization. One of King's best. But I don't agree with King's position concerning what happened to JFK.
I'm not sure if Stephen King has ever directly stated that he doesn't believe in a global conspiracy. He does, however, cast the subject in a dismissive light within the narrative of several of his novels. King either doesn't agree that there is a global conspiracy...or else he is aware of it but keeps his mouth shut about what he knows. He's a public figure, and to maintain that position, he can't alienate his readership, so he has to watch what he says.