Thanks for the picture, the date is a bit later than the 1950s. The office block (bottom left) was officially opened on 12th October 1971 so my guess is early to mid 1970s.
The older, lower, building to the right of the office block was the restaurant and kitchen. The car parking area to the left of the restaurant was the site of the original Rivers Mill House, unfortunately demolished. The large factory in the background was the stores, assembly area, winding and fitting shops. To the right are the old zoneworks buildings.
No doubt you have some stories about all these buildings?
Andy - Dursley Glos Web Admin