I've also wondered how you got on with Astral navigation if you were in 8/8 cloud for a sustained period. That DC-7C rumbling along at probably 25,000 feet was probably even worse than a jet for this.
and also the Britannia, answer is - not a lot, see post 43. On that occasion the Loran was available until crossing the coast, after that no Loran, no Astro, no NDB's. After that just maintain a good AirPlot and hope that the forcast winds were accurate. ( no other means of measuring groundspeed at that time. INS ? GPS? just a gleam in someone's eyes, maybe.)