European Panteras were called GTS then.
The US GTS would have GT in the serial number.
European cars could have been built with some options not available on US cars such as a steering wheel or a Holley carb.
In fact Group 3 cars were essentially European street cars with performance options added by "the factory" and I suppose even a dealer like Dubois?
The original invoice would be the only way to tell now and yes, Marti only has Ford's US sales records.