When I joined IBM, in 1968, I worked out of Wichita, KS., for about 4 years, and the huge Boeing plant was my primary account. They were building KC135's at the time. In the Summer of 1969, Boeing brought one of the first 747's to Wichita, and let it sit on the tarmac for several days while they tested the onboard AC and avionics systems under extreme heat conditions. That thing was Huge...I remember seeing it taxi behind a row of large hangars, and the cockpit was higher than the hangars. When it left, a few days later, the entire area was clogged with traffic and onlookers who wanted to see that big plane go airborne.
Sadly, Boeing closed that plant in 2013....after about 85 years of production.