The University of California Press edition of The Works of Mark
Twain, _Adventures of Huckleberry Finn_ contains a a discussion of
the existing proof sheets for Twain's novel.  "Two partial sets of
proof sheets have been preserved" (p. 799).  There is a lengthy list
of what exists and there is discussion throughout the annotations of
Twain's use of the proofs and changes he made on them.

Barb