While I have not had any work done at Bob Jefferson's Shop (North Brookfield, near Sturbridge) I have had some up-close-and-personal experience with his mechanical work on a couple of cars that I play with from time to time. A good friend has a Derby Bentley that had a mechanical rebuild by Jefferson's and he has run the car over 30,000 miles with nothing other than routine service. We have done plenty of other work on the car, but not anything related to the rebuild at Bob's shop. I have also found Bob to be a knowledgeable and willing source of information when I have had questions about Rolls-Royce or R-R built Bentley cars. The main complaint I have heard over the years has been the speed of the work (or lack of it), but I suppose that could be said of many shops including my own. In your case, as the work is already done, that is not an issue. If you were to call Bob, I'm sure he would be very willing to share whatever knowledge he can on the car you are looking at.
I hope this helps a bit.
Jon Lee