IIRC during the model year 1968, the GT package required a 4V carbureted V8. Since the "C" in your VIN represents a 2V carbureted 289 , it is unlikely that your car was a factory built GT model. As for the rest of the data, contact Marti Autoworks in Arizona for a "Marti Report" which would provide you with the statistical details of your car's build taken from Ford's production records. Most folks here consider the Deluxe report money well spent. If you want the full deal including a reproduction data plate and window sticker as well as a "one of ..X.." analysis, the Elite Report is also an option.
*67 Vintage Burgundy 390GTA has moved on to its next caretaker*