As a "native Missourian" I'm aware of all the discrepancies between
spelling and pronunciation.  Twain even prefaces Huck Finn with an
explanation of the different dialects used.  However, he does not always
spell a word the way it is pronounced; nor does he always spell it
according to the dictionary.  For example, in Pudd'nhead Wilson, he
spells St. Louis, Sent Louis--the way it is pronounced by many in the
region.  However, in Huck Finn, he spells Cairo according to the
dictionary spelling when it is pronounced by natives as "Kayroh"--like
the syrup.  Even Missouri is pronounced in two ways, depending upon where
the Missourian is from.   Around the turn of the century (according to
the book _Down in the Holler_ by Randolph and Wilson) "Missourians were
wrangling about the pronunciation.  'Nobody says MISS-SOU-RY but the
puritans and softheads,' wrote a prominent newspaperman.  'The correct
pronunciation is MIZ-ZOU-RAH.'"

So, to get back to "smouch," according to the above quoted book, "The ou
of "snout" is pronounced so that the word rhymes with "shoot."   A
"snout" is pronounced "snoot."  This is the closest reference I could
find to "smouch."  My MIZZOURAH guess would therefore be that it was
pronounced "smooch."   Twain had, after all, a "Mizzourah aksint" rather
than a  Southern drawl.