Pretty sure that XV205 had a Litton Inertial Navigation System, as mentioned I flew it (alongside an OCU Nav) for the GW1 flyby practices and on the weather-cancelled actual day of 21 June 1991 (according to my logbook the Captain was OC 242). As an IN platform it had Ring Laser Gyros and I still have the notes on firing it up somewhere.
For a while Navs could go to Ops and sign out the hand-held PLGRs which operated from an aerial deployed through the periscope sextant housing. Those were the days when the US military limited the availability of precision-acquisition codes to certain accredited operators (of which the RAF was one) and before the opening of the system to wider use. Chickenlover may even remember me using my own hand-held GPS to decipher some US reporting points on the way back from Guyana to Charleston via Rosie Roads (24 Nov 97).
Whilst flying in GW1 during the period immediately after 16 Jan there was some chat amongst the Riyadh-based crews about putting tinfoil strips behind the air-deflectors for a single-shot chaff dispenser but I found the locally procured Bacofoil more useful to make hats with.
As has been said, memories can be suspect but I'm reasonably sure of my recollections as I was operating the kit.