I've been doing a bit of research on the early Topps cards and also a little on Gum Inc and Bowman. I found this real estate listing from 2008 which shows the Gum Inc plant!
http://www.metroflexspace.com/gum_factory.html
Click around a bit, there are some different views on different pages.
The address is 4837-49 N. Stenton Ave in Philadelphia, just down the street from # 4865, which is where Bowman was located. The latter building is now mostly demolished though:
http://toppsarchives.blogspot.com/20...les-force.html