Why not if his theory is absurd and baseless? No reasonable person can believe that the plan was to frame Oswald by linking him to a specific rifle and shooting location but then using a different rifle and shooting location to commit the assassination. Why do that when the conspirators could have just used Oswald's rifle and fired the shots from the 6th floor? Thereby eliminating the incredibly risky and complicated necessity of stealing the president's body. Of all the far out CTer theories, the most outrageous is that someone stole JFK's body and returned it before the autopsy. That is tin foil hat stuff that should be rejected without reservation by everyone.
According to his friends/colleagues, Lifton himself, he was working on an updated/new book - "Final Charade" - that included a claim that Oswald was a willing participant, a conspirator, in the assassination. He wasn't framed and/or an innocent bystander. Lifton's claim was that Oswald was indeed in the "sniper's nest" but that his role was to stick a rifle out the window and fire blanks at JFK.
Why he was supposed to do this is a mystery. Why he went along with this is another one.
To take a step back at this whole conspiracy idea: JFK had enemies in the government, he also had friends. And he also had people who may have disliked him but wouldn't go along with murdering him, essentially committing treason. How any conspirators planning this in advance would know which was which, know that some people they asked to go along with this wouldn't, would expose it before or certainly later after it was done, is something that I've never heard explained by the conspiracy believers. As in: "How could you possibly plan this out and know it wouldn't be revealed?"
Lifton's discussion is here: