It is also a good sign that it is a authentic GT/CS since these cars tended to be done in punches. This way workers could put on the CS parts, drill the required holes, and cut out sheet metal (rear panel lights) on many cars versus just one or two.
Doug
PS. my coupe (non-CS) and CS are only 250 VIN #'s apart and are twins as far as color, engine, transmission, and interior (minus A/C). Remember the VIN #'s don't actually mean when they came down the line but when they were placed into the Ford system. You can actually have a later # and it was built before the earlier one, this is especially true with the CS because of the special parts.