Following on the heels of the MX-1964 mockup was a mockup of the B-58 as it more or less was built. Clearly built in the same facility, what’s unclear from the photo is whether any components from the previous mockup were re-used. All the major components appear to be substantially altered, so it might have been an all-new structure, or it might have used some of the same internal supports. It would be nice if such things were able to be preserved, but mockups like this usually wind up getting turned into firewood.

The Convair B-58 Hustler grew out of a long series of design studies dating back to the years immediately following World War II. Early concepts called for small jet bombers carried aloft by B-36 or B-60 bombers, and would shed jet engine pods during the mission. These massively complex and expensive systems evolved over time to the somewhat more straightforward B-58 which was a single stage aircraft carrying an underslung pod containing both jet fuel and a single nuclear weapon. But even that was originally intended to be a rocket powered missile.

The B-58 evolved directly from the MX-1964 design from 1952. This is recognizably related to the B-58, but had the four jet engines in two pods rather than four, and a higher degree of integration between the pod and aircraft.