Gane

We have inherited a Jaguar S type which my father-in-law had made notes that it was registered 4 months before the Browns Lane production line started building the S type. It was owned by Jaguar for over a year and he thinks used as a prototype test car at Jaguar. The VIN is SAJAC01FXXGL20900 he noted the X means The Whitley Engineering Centre in Abbey Rd. Can anyone confirm this? and have any further info please? The car is now for sale. Thanks Ivan