I take it that Mr. Halperin is referring to Howard Baetzhold's _Mark Twain
and John Bull_.  The original poster might also check Baetzhold, Howard,
"The Course of Composition of _A Connecticut Yankee_: A Reinterpretation."
_American Literature_ 33 (May 1961): 195-214.

Note, too, that Twain wrote a letter to "Mother" Fairbanks in which he
solemnly promised that the characters of the Arthurian legend would
emerge from the pages of his novel as noble and pure.  I have never
read anything concerning her response to the book, but presumably she
could not have been very happy.

Concerning the "Injun Joe" question.  Injun Joe is a half-breed.  This makes
a certain amount of sense, given Twain's conscious recreation of the
Theseus/
Ariadne myth in on.  (The Minotaur, too, has a double nature.) I
particular version. (The Mintaur, of course, also has a double nature.)
iness.
I suspect it doesn't matter much.

Bob Champ