The only other Comet I know of to have had any involvement in Nimrod was an airframe built specifically for cabin pressure test work in the water tank at Farnborough, after a simulated 100,000 flying hours the fuselage was taken to Woodford and used as a mock up to house the Nimrod MR1 as well as having wooden panier skirts fitted.
Once the above work was complete the airframe was used for smoke egress training by the Woodford Fire department.
In 96/97 the fuselage was moved to Warton and modified to MRA4 fit in way of flying controls/ hydraulics and used as the "Iron Bird" for endurance testing of the FCS, the cockpit section came from an ex AEW aircraft XV263 as the old Comet front end had quite a bit of structure missing - I can't remember the actual build number of the Comet it was something like 5402 - Mike