Boeing soon realized that this would not provide a sufficient payload, so the fuselage was widened to 144 in (3,660 mm), the same as the KC-135 Stratotanker, which would allow six-abreast seating and the shared use of the KC-135's tooling
Shared tooling was to have been the case if the 707 & 135 shared the same fuselage diameter, but they didn't, so difficult to see how they shared tooling. Boeing themselves say,
The Dash 80 prototype led to the commercial 707 and the military KC-135 tanker. Both planes shared the basic design of the Dash 80 but were very different airplanes, neither one being a derivative of the other.
The only similarity between the -80, 707, 135, is the looks.
Are you sure about that-?? The ' upper floor' stresses would be significant whereas in a tube, hoop stresses are much easier to handle and uniform ...
CONSO, The below floor area of the 135 is unpressurised, except for the area immediately below the cockpit, and of course the boom operators compartment at the rear.
the early models of KC used water injection for takeoff
As did the early 707 and 747.
