According to the ad 9193 is a 1979 car. The euro GTS's actually had performance modifications. Higher compression, solid lifter engine, bigger wheels, suspension improvements. The US GTS's had cosmetic add ons like fender flares, paint scheme, etc.
http://www.panteraplace.com is a great resource. In the technical section, near the bottom, is a link to a good buyers guide. There's also a registry at http://www.provamo.com but you have to register a De Tomaso (ANY De Tomaso, yours or not) to become a member.