Until now, I have differentiated Pastor Russell's pyramidology beliefs from the pyramid that was erected next to his tombstone in Pittsburgh, Pennsylvania. Russell (following Taylor, Smyth, Seiss and Barbour) believed that the Great Pyramid of Gizeh was "the Bible in stone," testifying to scientific and theological truths. The pyramid marker at his grave I believed was not related to his beliefs on the Great Pyramid, but were an elaboration of the plan of salvation as Russell understood it.
However, an ebay auction has just closed which contained the program for the 1921 Annual Meeting of the Watch Tower Society held in Pittsburgh. Russell's tombstone and the pyramid marker had just been completed. (The 1919 Convention Report shows the plans for these items but construction had not even commenced then.) The 1921 program contains several pictures of both the tombstone and the pyramid. The listing can be seen at:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rd=1&item=260151336489&ssPageName=STRK:MEWA:IT&ih=016
(You may have to sign in to ebay to view the listing since it has expired. If the link doesn't work, then paste the listing number 260151336489 into the search box on ebay. That should bring up the listing.)
There are several clear pictures of the 1921 Annual Meeting program on that page. If you want to save these, I'd recommend saving them to your computer as this program is extremely rare and the listing will eventually cycle off ebay.
One of the pictures contains an explanation of the building of the pyramid and I was surprised to see this statement (which can be seen at the ebay site):
"The capstone, itself a perfect pyramid, is patterned after the capstone of the Great Pyramid of Egypt, symbolic of the Christ."
So, one can say that the capstone of the pyramid marker at Russell's gravesite is modeled after the Great Pyramid of Gizeh, right?