Link below to an anticle in The Telegraph (English newspaper) about the making of the film, and a look at Disney's Animation Research Library (ARL) in Glendale, CA. Learned that the original script was often dark and serious, more like the classic Disney from the days of Pinocchio and Snow White. Walt scraped it and went with a new script that was the lighter, lively, jazzy version that was made.
Also that The Shermans tried to get The Beatles to sing "That's What Friends Are For" - done by the 4 vultures with English accents and Beatles haircuts in the film. Legend has it that John Lennon refused saying "I don't want to do an animated film". 3 years later they did Yellow Submarine.
Moving to more recent Disney films the ARL Creative Director says that Ursula was thought of as a combination of an octopus and "Joan Collins in Dynasty". Exactly!
The Jungle Book: the making of Disney's most troubled film - Telegraph