Thanks to all who have responded to my inquiry.  I'm a very casual
follower of this list, and I really appreciate learning about the
archives--should have looked there first.

Having read most of the archive references from the Spring of 1996, I'll
only add that a couple of additional pieces of information are included
in the latest "Acoustic Guitar" magazine piece.  First, they claim the
provenance has been authenticated by an address label or some such that
has existed with the guitar's case--I think this has Twain's handwriting
and signature. Second, someone has done the appropriate Martin research,
because the model number and the date of manufacture have been
determined--it apparently has been verified as a Martin guitar made in
1835 by C.F. Martin.  The article is very short, but it also describes
the original case, which is the "casket" type (these really look like
little caskets of the same period) that would be correct for that
vintage.

Someone mentioned back in `96 that the guitar looked "pretty beat up,"
but I must say that, given the vintage and the fact that Twain evidently
dragged it all over creation, I think it looks spectacular.  I think you
all would enjoy seeing the nice picture.

Best,

Tim