Dear Steve,

  Twain himself or his characters or his (actual or imagined)  
manuscripts appear in the following novels, stories and plays:

*Jap Herron* (1917) by Emily Grant Hutchings
*Return of Mark Twain* (1918) by Eunice Winkler
*Murder Stalks the Circle* (1947) by Lee Thayer
*God Bless U, Daughter* (1968) by Mildred Burris Swanson
*Silas Timberman* (1954) by Howard Fast
*The True Adventures of Huckleberry Finn* (1970) by John Seelye
*The Fabulous Riverboat* (1971) by Philip Jose Farmer
*1876* (1976) by Gore Vidal
*A Bloodsmoor Romance* (1982) by Joyce Carol Oates
*The Further Adventures of Huckleberry Finn* (1982) by Greg Matthews
*The Day They Came to Arrest the Book* (1982) by Nat Hentoff
*I Been There Before* (1985) by David Carkeet   (my favorite of the  
bunch)
*The Boys in Autumn* (play) (1986) by Bernard Sabath
*Never the Twain* (1987) by Kirk Mitchell
*Scavengers* (1987) by Yvonne Montgomery
*Huckleberry Fiend* (1987) by Julie Smith
*Twice Upon a Time* (1988) by Allen Appel
*If I Never Get Back* (1990) by Darryl Brock
*Death on the Mississippi* (1995) by Peter J. Heck
*The Great Twain Robbery* (1995) by Robert Guntrum

[I discuss all of the above in *Lighting Out for the Territory*(1997)]

Other works I came across after my book came out include:

"More than a Reader's Response: A Letter to De Ole True Huck" (1995)  
by Gerry Brenner
*Tom's Lawyer* (2001) by Peter J. Heck
*Test of Time* (2001) by Charles Harrington Elster [this imaginative  
time-travel adventure story that incorporates vocabulary from the SAT  
and the ACT is
 written by a former student of mine from Yale;  it makes a good gift  
for high school students]
"My Jim" (2006) by Nancy Rawles
"Finn" (2007) by John Clinch

All the best,
Shelley