I would have thought that these more modern types could have fulfilled most of the tasks of that era, so why did it remain in service for so long?
Interesting that that the Hastings, which was replaced by Argosies and Britannias on various transport squadrons should outlive the Argosy, Comet and Andover (C1 at least) and lasted about the same time as the Brit (1977 I believe). As storl tern implies it was a case of, if it aint broke, don't fix it, and there was no temptation to do an expensive refit on any of the types you mention.
Small point, in 1967 Transport Command was renamed Air Support Command and this in turn became 38 and 46 Groups in 1972. Pedant mode switched off now!