I'm wondering if the lower aircraft in the middle picture is a Trident 3. For many years after their withdrawal G-AWZU was kept at Stansted and used for tug driver training. Engines removed but cowlings remained. It was kept nicely clean and retained its livery apart from the BA titles being removed. It could be seen parked at various gates of the new terminal and looked remarkably complete and ready to fly if you didn't know it or look closely. I always looked out for it. Believe it was finally scrapped in 2003.
Regarding DC8s there, I arrived back in the early 1990s on a humdrum Air UK 146 from Edinburgh, we parked alongside an MGM Grand DC8-62. They were a notably high end US operator with an all first class fitout, who ran schedules from New York to Las Vegas and Los Angeles for the wealthy. Must have been a charter over to London.