Despite some Dodge advertising with big, bold letters adding up "GT + 383 = New Dart GTS," Tony's car wears only GT badges, a fact confirmed by the paperwork of his car. In 1968, when A-body 383s saw a bump in power to 300 hp, the model officially became the GTS. Even though the car is often called a GTS today, these early production models--made available from March 1967--are technically just Dart GTs, but small "383 Four Barrel" call outs on the fenders allude to the thundering engine under the hood.
https://www.hemmings.com/magazine/mus/2014/02/Do-the-Math---1967-Dodge-Dart-GT-383/3735001.html