ByJohn McClenahen Beginning Sept. 4, Boeing Co.'s senior executives will work from new headquarters offices at 100 North Riverside Plaza in Chicago. "It was a very difficult decision, and no single factor made the difference. In the end, we looked at all the data and made what we believe is the right choice for Boeing," says chairman and CEO Philip M. Condit. On Mar. 21, when he announced that Boeing would move its headquarters from Seattle to one of three cities --Chicago, Dallas/Ft. Worth, or Denver -- Condit said that Boeing's new headquarters needed to be "in a location central to all our operating units, customers, and the financial community -- but separate from our existing operations." From the beginning, only Chicago seemed to meet the financial community criterion, although among corporate relocation experts, because of its better weather and business dynamism, Dallas/Ft. Worth was the heavy favorite for Boeing's new world headquarters.