First, check Tom Tenney's extensive Mark Twain: A Feference Guide. (G.K.
Hall).  Then
check Tom's supplements to it in American Literary Readism, I think from
1977 to 83.  He has also
added much in most of the Mark Twain Circular's "About Mark Twain" section
at
the back of many issues.  For easy use of all this, consult my
index of all this here on the Forum or in various issues of the Circular.