Seegee:
If you want to read more about a fictional version of Twain I recommend Philip Jose Farmer's Riverworld series,
I'm glad you brought that up, SeeGee. I read the first of the
River World series when it first came out. Found it marvelously inventive and interesting. Loved it, and could not wait for the next installment. The second book, I thought, was not so good, but I figured that it would get better with the next. Nope, for me at least, it was worse still. My impression was that Farmer had this great idea for a setting for a book, the River World, but then once he had it fully established, he had no good idea what to do with it.
Might just be me; I had the same feeling about the whole
Dune line of books.