I'd get in touch with the Rolls Royce Owners Club (www.rroc.org/) - they'll be able to help you identify the car. Initially, they were just long wheelbase Shadows but after a while got the name Silver Wraith II. As well as the longer wheelbase, they're often identified by a smaller or even deleted rear window. They also have a vinyl roof - but this was an option on Shadows. Tracing the history of a car is tricky, but if the car is known already to the club they may have some info.