The UK E3D is based on the Boeing 707-320B series airframe.
The KC-135 was based on the 367-80 first flown in 1954. This was widened from 132in to 148in for the 707-120 flown in Dec 1957. The 320B was fitted with extended span wings and an 80in fuselage stretch, first flown in Jan 1962.
https://en.m.wikipedia.org/wiki/Boeing_707#Development
Boeing 707-320, 707-420