These were the last 3 KC-135As off the production line, all 1964 models, 64-14827, 64-14828, and 64-14829. All were converted to the KC-135R standard in the 1980s. Once the RAF conversion begins, the USAF MDS will become RKC-135Rs until the Boom equipment is removed, then RC-135K for the RAF. The RAF tail numbers will be ZR135, ZR136 and ZR137. They will be stripped right back to bare metal and new metal introduced where needed. They will also get new CFM-56 engines and an updated avionics suite (front end and back end!). Other mods will also be carried out to bring them up to required standard.
Now they could go to the effort of smelting down all the metal and rebuilding it again but why bother if the structure is sound? It reduces cost and carbon footprint!
iRaven