I'm absolutely loving this thread and have just wasted (not really!) over an hour absorbing it. Looking forward to the book.
There were a bunch of intrepid aviators still doing some of this stuff in 4 engine jets up to the early 90s - the RAF's Victor crews. We frequently crossed the Atlantic with the minimum required 2 long range Nav systems - the Omega and the Navigator. Someone convinced the authorities that he qualified as one - although the accuracy varied considerably depending on several factors, included numbers of beers consumed the night before.
The reason Tankers still used Omega was that if two aircraft wanted to get together a long way from radar or short range land based systems, Omega would give both aircraft the same error and they would meet up. Some Victors were fitted with a single Carousel in the Falklands war, but there was only room for one system, so Omega stayed.
The other Nav kit consisted of one ADF, one TACAN, the Doppler fed Ground Position Indicator and the original Nav Bombing System fed from the WW2 era H2s Radar. One day crossing the pond, Omega dropped out to to a solar storm, we were out of range of the NDBs, we couldn't pick up Consol, the sea was silky smooth - so no Doppler and out of range of radar fix points - so our intrepid Vasco broke out the sextant. We coated in 32 miles off track, which I thought was quite good, but Shanwick didn't agree and violated us. No one was daft enough to let us into MNPS airspace, so luckily we were a FL450 where no one else was.