Rockwell decided to build the Orbiter Mockup for the same functions - (training and engineering design concept checkout). The mock-up was first shown to the press and public in the first week of March 1974. As time went on, NASA paid for the building of the "Iron Maiden" (A tooling and design fixture) in the manufacturing area. It was built to the design drawings with all of the hardware installed in the exact locations that were defined for the flight articles. It was used for years by the engineering community to actually see where a design change would be located and to assure that the hardware would be compatible with surrounding hardware.
In the meantime, the public relations department took over responsibility for the DEI room and it became the location where we held all of our major design reviews. The Engineering Crew Equipment people continued to use the crew compartment of the mockup for checking out the various pieces of hardware that they were developing. Among other things a mockup of the crew escape system which Rockwell proposed following STS-51L was installed and was used to develop the proposed concept. The same thing was done when the "Sleep Stations" were undergoing the development process. At various time there were mockups of a wash station and various configurations of storage lockers.
At one point in time the Air Force was supposed to have had jurisdiction over the mockup. I am told that they were using it for design evaluation while they were still looking into procuring several Orbiters for their use at the Vandenberg facility. If the USAF had "jurisdiction" over the mockup in the DEI, there was no obvious indication(s). It was accessible most of the time (occassionally it'd be closed-off due to some modifications being done in it). When they decided against that procurement and the use of VAFB as a launch site, custody of the mockup reverted to Rockwell.
By this time it had become the centerpiece for most of the Public Relations activity. The former head of Public Relations told me that he seemed to recall that, at one point in time, the Japanese had even offered to buy the Mockup for a sum in the neighborhood of 1 million dollars. As best he could recall, he thought they planned on using it for a museum display or something like that. I have been unable to confirm this.
As you can see (on the photos on this page),the mockup still has the original design concept for the OMS engines, i.e. a fairing for the OMS pods extended onto the aft payload bay doors. This design was abandoned very early in the development phase and the pods were designed to be fully self contained and located aft of the payload bay doors. And also the forward RSC thrusters are protected by doors.
As to the future of the mockup, the only thing I have been told is that there are those who want it to remain at Downey for "historical" purposes. As far as Boeing is concerned, I believe they have relinquished any responsibility for it. As it now stands, the entire Downey facility has been shut down and a majority of the tooling, parts and materials that were there have been moved to a government storage site in Compton (a suburb of Los Angeles).
"Me" at the controlls on the aft-flight deck of the "first" Space Shuttle. If you look closley at the aft area of the flight deck, it shows just how non-high fidelity the mockup truly was that area is incomplete!!! On most Missions that part of the flight deck is used for payload control pannels (like the IUS).