There's also Dudbrook Hall, Navestock, near Brentwood. This was the former home of the Waldegrave family. I'm unsure of its 20th century history, but I do recall that when I moved into the next village 20 years ago it was a retirement home (it still is). Whether it was like that in the 60s, I cannot say.
Google for it and you may find some information.
Phil
historyhouse.co.uk