Norfolk was both very simple- in that there weren't many changes- and very annoying- in that I had to reconstruct vast amounts by hand because the maps weren't on the LGBCE website.
And here's Essex in '74. So that's the East of England finished.
Greater London will be both straightforward - as it's all boundary changes between boroughs and a single parish- and potentially a bit tricky if I decide I need to do an enlargement.
Apparently I never actually posted this here. It's the point of creation in 1965 rather than '74 so this is officially the furthest back I've gone with this series.
And moving into the South East with the various workarounds I'm now doing, here's Buckinghamshire.
Milton Keynes is one of the areas that has, understandably, changed the most since then- and has actually ended up with more parish councils as the city has grown.
One that should be of interest for @AndyC and @Mosak at least: Oxfordshire 1974. Probably the most surprising thing in retrospect is that Oxford didn't annex anything from Vale of White Horse when they did their big expansion in 1991.
Having seen just how much of the north of the county is unparished now- and that's after some of it was parished in the 90s- I can really see why the Greater London border in Surrey was originally meant to be so much further south.