I haven't read Lifton's book, and I don't want to imply agreement with any particular claim, but he is certainly correct that there were lots of implausible details about the autopsy, and especially with the official summary of the autopsy. It wasn't a physician who came up with the "magic bullet" theory, it was Arlen Specter, a cipher whose later continuing political success is inexplicable except in reference to his role on the Warren Commission.

The best book to read now is JFK and the Unspeakable, by James Douglass. If a book like that doesn't fit into your life right now, either of the recent Oliver Stone documentaries are great. I believe that "JFK: Destiny Betrayed", which I watched through tears, is a longer version of "JFK Revisited: Through the Looking Glass".