Which could, effectively, be considered a fixed datum.....

I don’t know what you think you saw in the Nimrod R1, but it had the system I described in my previous post. My fault I didn’t make it clear. Carousel was standard fit through the late 60s and 70s for aircraft such as 747. It was fitted in Concorde and also in RAF VC10s and Sentry.

it was a very good system. I believe a single unit was used for FI. Units were also borrowed for the famous pics of Nimrod MR2 meeting up with the boats at the pole.

Salad - At the time (1972 or 73?) I wasn't given the name of the actual unit - just shown what was a very large piece of kit in the R1 at Boscombe. For obvious reasons we couldn't photograph it but we did have a 30-45 minute discussion on fitting, reliability and use. I'm pretty sure we were told it was at least a double unit

A Carousel would certainly be the answer. I saw commercial ones later but they didn't seem as bulky

The Falklands Vulcan had a triple installation "borrowed" from BA I think - but that may have been a later, smaller unit

If you Google "delco carousel" there are some interesting links - unfortunately most of the pictures are of the control & display unit not the actual gubbins down the back.

IIRC the OP Corporate Vulcans had a Twin Carousel fit using borrowed VC10 kit. The boxes were mounted on the bomb aimers window cover and made getting into the radome a right PITA.

Most sources refer to BA 747 kit but I can't find anyone saying they actually came from there . I can imagine shoehorning that kit into any aircraft at short notice would be a challenge!

The VC10s had been bought from civvy sources and were in storage at Abingdon awaiting tanker conversion. As you said, twin fit for the Vulcan, the Corporate Victors had a single fit Carousel or a single Omega, some had the standard kit with no enhancements.