Does this help a little:
http://www.jwstudies.com/Changed_MD_and_SS_words.pdf
Also, the diagrams showing the "Dispensations" and of the Great Pyramid in the Millennial Dawn/Studies books provide additional clues. He called the series Millennial Dawn because he considered that it had already commenced. Imagine what the current WTS would do to him if he was preaching his message today!
The 1874 Parousia (discovered courtesy of Barbour) was still being taught as late as 1930. The date of 1914 was the end-point of the unprecedented Time of Trouble, which would see the outbreak of world-wide peace under the auspices of Zionism. 1874 and 1914 this provide the meaning to his magazine title: "Zion's Watch Tower and Herald of Christ's Presence" - one part related to Zionism's future and the other part related to the fact that Christ's Parousia had already taken place.
Doug