I don't know whether Stalingrad was a book, but I think THE HOODS is the only novel Leone turned into a movie. Did you ever read any other books that made you think of Leone? Any novels you would have loved him to turn into a movie?
Why does everyone confuse Stalingrad with Leningrad?
Anyway, it was to be inspired by Harrison Salisbury's 1969 book "The 900 Days: The Siege of Leningrad"