This article, a rather lengthy and detailed conversation, is the most definitive thing that I have seen. It is probably not as detailed as you would like, but he does not talk about his work much. Here is an excerpt:
“No, no, no,” Bob Dylan says sharply when asked if aspiring songwriters should learn their craft by studying his albums, which is precisely what thousands have done for decades.
“It’s only natural to pattern yourself after someone,” he says, opening a door on a subject that has long been off-limits to reporters: his songwriting process. “If I wanted to be a painter, I might think about trying to be like Van Gogh, or if I was an actor, act like Laurence Olivier. If I was an architect, there’s Frank Gehry.
“But you can’t just copy somebody. If you like someone’s work, the important thing is to be exposed to everything that person has been exposed to. Anyone who wants to be a songwriter should listen to as much folk music as they can, study the form and structure of stuff that has been around for 100 years. I go back to Stephen Foster.”