A trivia bot claimed that on October 27 1988 Larry Flynt paid a hitman $1M to kill Hefner, Guccione, and Sinatra. A web search (including searches at The Smoking Gun, snopes.org, and The Straight Dope) tuned up nothing, except copy-pastes of that factoid. No confirmation, no debunking. I’m not even sure where to look for more info, except perhaps library newspaper archives.
Is this true? What’s the rest of the story?
I think you’ve answered your own question, really.
I’m sure that if such a thing were true and that anyone other than Flynt and his inner circle knew about it, it would have made the news big time. Hefner is pretty outspoken and he’s been asked about Flynt twice in recent years in a published interview in which he was asked about Flynt and also Guccione. In the interview he talked about Flynt having published photos he’d acquired of Hefner having sex with a former girlfriend who was now married with teenage children and that Flynt faced heavy litigation as a result. He also said he thought Flynt was what he said he was…a hustler. Based on the way he’d heard Guccione treated people, he seemed to think a lot less of Guccione than he did either Guccione’s son or Flynt. So I doubt the hitman story is true.
I realize this is an old thread.
Here’s the link to the L.A. Times article.
Even if it’s not real, I think it’s a funny notion that the murder plot was foiled because Flynt’s business manager stopped payment on the cheque to the hit man. 
And we’re supposed to believe it’s just a coincidence that Flynt paid to have Walter Annenberg, Bob Guccione, and Frank Sinatra killed and they’re all now dead?