Sorry - it's been a long while. Busy, busy and not much to say, I guess. Thanks to two history students prodding me, I've finally uncovered the story on the safe! (It's no longer a summer research project!). Thanks to Diebold company's 150th anniversary website (2009), the answer was easily found. According to their information, the company moved to Canton, Ohio and was named Diebold, Norris, and Co from 1874-1876. I finally had a manageable date to work from! Prior to this, I only knew it was purchased between 1864 and 1926 since the name on the safe was North-Western College.
I checked our newly transferred financial records from that time period and after skimming through everything from those years, found an entry in August 1876 for $200 for the purchase of a "new office safe". Since no more details than that are available, I'm making the leap that that is the one and same office safe that now lives in the archives reference room.