I finally talked to Mark Winegardner the other day and here are some tidbits:

He says the synopsis on the Amazon.co.uk site was taken from a proposal before the book was written, so it's not entirely accurate. He does say it takes place between 1955 and 1962, however, so it's not quite a "sequel" to Godfather Part III as much as it's a sequel to the NOVEL itself. He claims it does not interfere with the movies, tho he did take some minor liberties that expands on Puzo -- and wraps up some things that Puzo left out. He says there will be some deep in-jokes for the true fans. The book will start with the murder of Tessio.

I asked about a possible movie, and he said he had no idea what Paramount's plans would be. He's not really interested in the movie-making aspect of it. He just wanted to write a good book, and he says his style evoked the style of Puzo without imitating him.

He said it felt great following in Puzo's footsteps, because Puzo is a wonderful story teller. He wasn't "nervous" about it, but simply wanted to write a book that people would want to read. Like Puzo, Winegardners says he's read about 100 books on the Mafia as research, and really wanted to bring more of the mafia aspect into the story.

Interestingly, he also said it worked out that The Godfather Returns has the same number of books and chapters as Puzo's novel.

Winegardner spent every-other month or so at the Yaddo artists community, where Puzo himself spent some time writing. As the Director of Creative Writing at FSU, Winegardner teaches advanced graduate students. There are 3 televised interviews with him here , near the bottom of the page, that you may find interesting.

It was great speaking with him, and he hopes that everyone enjoys his book!