A recent thread about the DC-8 in CivAv suggests that, after extensive redesign from the failed tanker program to commercial production, the plane was made marginally wider than the 707 and had 6 abreast seating.
I've always thought that the DC-8 and DC-9 had had a structural relationship similar to that of the 707, 727, and 737. That is, the DC-9 shared the same cross section dimensions (and a very similar nose) as the DC-8 even if the two don't share the "same" fuselage. I seem to recall that DC-8s and 9s all had 5 abreast seating because they were actually narrower than the 707/727/737. Am I simply wrong? And either way, what exactly is the relationship between the DC- and DC-9 fuse?