I'd also add:
Leonard and Tenney's *Satire or Evasion?: Black Perspectives on Huckleberry
Finn* and Shelley Fishkin's *Was Huck Black?: Mark Twain and
African-American Voices* to the list of Chadwick-Joshua's book as excellent
sources for information on this topic.
Something else that might be worth exploring, if it hasn't already, is the
impact of Hemingway and Paine's use of the phrase "nigger Jim" when talking
about Huckleberry Finn and perhaps the rise of racial concern about the
text.
Michael MacBride
Southern Illinois University, Carbondale