https://en.wikipedia.org/wiki/Willis_Tower#History
http://replicabuildings.com/proddetail.php?prod=730
https://en.wikipedia.org/wiki/Willis_Group#Buildings
...the 605 ft (184 m) tall art deco-styled building opened on June 9, 1930.
https://en.wikipedia.org/wiki/Chicago_Board_of_Trade_Building#1930_building
https://en.wikipedia.org/wiki/Chicago_Board_of_Trade_Building#Position_in_Chicago.27s_skyline
http://skyscraperpage.com/diagrams/?searchID=75218397&offset=25
https://www.google.ca/search?q=One+North+LaSalle+Chicago&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi9lIX_gPHQAhVE7WMKHVtxDAsQ_AUICSgC&biw=1538&bih=738
http://explore.chicagocollections.org/image/uic/59/5x25j4z/
https://en.wikipedia.org/wiki/List_of_tallest_buildings_in_Chicago#Tallest_buildings
jh
http://replicabuildings.com/proddetail.php?prod=900
