Chevithorne housed the English department in 1965 and continued to do so until 1983. It was a large country house with significant land on the north side of the A30 opposite the main gates into the college. I think the images I've included here are of the right building but never having seen it I cannot be certain - so if you know better please do let me know. "Chevithorne" is no longer included as one of the buildings at the college; it may be that it has been demolished or redeveloped and renamed.
There are references to several other buildings in the same approximate location including a Brantwood and a Mount Royal. Nowadays the building(s) in that location are referred to as Wettons Terrace housing the Music Department and International Study department. There are also some pictures in the Charles Miller collection of photos that seem to be of the same building but refer to it as the Music Department building and gardens. If anyone has some pictures that they know to be of Chevithorne or who have a clearer memory of what was where then please let me know.