Interesting. I do have the complete set of Russells Studies in the Scriptures and the Divine Plan of the Ages.
Heres a passage in Volume 3 regarding the Great Pyramid and various measurements of its interior, and its significance with the 1914 AD date:
"So, then, if we measure backward down the "First Ascending Passage" to its junction with the "Entrance Passage," we shall have a fixed date to mark upon the downward passage. This measure is 1542 inches, and indicates the year BC 1542, as the date at that point. Then measuring down the "Entrance Passage" from that point, to find the distance to the entrance of the "Pit," representing the great trouble and destruction with which this age is to close, when evil will be overthrown from power, we find it to be 3457 inches, symbolizing 3457 years from the above date, BC 1542. This calculation shows AD. 1915 as marking the beginning of the period of trouble; for 1542 years BC plus 1915 years AD. equals 3457 years. Thus the Pyramid witnesses that the close of 1914 will be the beginning of the time of trouble such as was not since there was a nation -- no, nor ever shall be afterward. And thus it will be noted that this "Witness" fully corroborates the' Bible testimony on this subject..."
Studies In The Scriptures, vol. 3 by Charles Taze Russell, copyright 1891