Hey! That mod facility was the United Air Lines Maintenance Center. It was scheduled to be moved to San Francisco (SFO) in 1942 but the war upset those plans. The Cheyenne tail for the B-17 was, I've been told, designed and prototyped by UAL engineers (under Boeing supervision) at the facility. We have a drop hammer at SFO that made the trek west in the late forties that looks exactly like the one shown in one of these photos. If it's the same one it was made in 1926. Since Continental management took UAL over (merger my butt) that hammer has largely gone dormant, it's sad to see skills and capabilities being tossed aside. At least there are a few of us who refuse to give up the English Wheel. Sorry about the ranting.