Some old newspaper archives exist (although some of them are a PAID service, be careful!), where you can view scans of the actual newsprint pages. If you are lucky enough to find the originals of your articles, you can compare to the "modern" versions and see if any content was edited.
I haven't the time right now to search, but give a try to some of these links. I found a number of Mark Twain pieces at these links some time ago.
http://nyheritage.nnyln.net/
https://www.nypl.org
http://lostmuseum.cuny.edu/archive/
I also ran across this link that looks interesting, but it has nothing earlier than 1836. But someone might find it useful for another project:
http://chroniclingamerica.loc.gov/
The Making of America collections at Cornell and at U of Mich are good, but I think they only have magazines on file.