I was at EEV from 1955 to 60 and can add something to your section on Cavity Magnetrons.
Development did not end with the death of Randall in 1941 (?) - Boot kept on working at SERL and about 1955 produced the'Boot' magnetron. This was adapted to high power working with no strapping, which was the seat of sparking and a block about a wavelength thick with much more thermal capacity. These measures gave the S band version a life of about 9,000 hours at 2.5MW output compared with the 500 to 1,000 hours and maybe 1 MW which was the wartime compromise between power and life.
The S band version was highly successful, used by MWT and DECCA and gave little trouble. According to a harassed MWT field engineer in Cyprus, the main cause of failure was the RAF taking it out of the Radar at any excuse and letting it roll off the bench!