Since I first posted about this, I've added more than a dozen links by
finding alternate period sources for some of the pieces that didn't have
digital access to that exact journal. By now the access rate looks to be
about two thirds - higher if you are at an institution that provides
JSTOR. I've also started adding some illustrations - just for fun.

For the long term, I'm looking at locating copies of the more obscure
works and digitizing them myself. That won't be any time soon.

http://terryballard.org/professional/twainjournals.html

Terry Ballard
New York Law School, Mendik Library
New York, NY, 10013