For Tolkien’s work, there is the twelve volume “The Complete History of Middle Earth” which is about as inside baseball as you can get for Tolkien.

I’d replace HoME with Parma Eldalamberon, Vinyar Tengwar and other journals publishing his early materials here.

Recommending Italo Calvino’s Six Memos for the Next Millennium, the lectures he has been preparing shortly before his death.

Not an assembly guide for a work of literature, but it’ll help your own process if it’s already ongoing and you want to improve.

The lectures also have some comments on what Calvino himself was doing here and there and why.