It's about three times the market value. The black and white photo came from an entertaining article in the MTWC Bulletin of about 1970 relating to a purported Yorkshire Road Race which was in fact a spoof, but which fooled a lot of people at the time. The article referred to the engine being tuned by Chaffinch Motors of Far Headingley, a firm that I understand was completely made up but which is blindly reproduced in the current advertisement! Such is life.

Tony