school me on differences between Dart, GT, and GTS?

1967 Dart 270 The 270 meant 'Series', which included an upgrade in Trim and Exterior Molding.

Typically found with;
* Lower Rocker-Panel Moldings
* Roof Drip Edge Molding
* Upper Body Side-Molding
* Trunk-Lid Molding

Engines
* 170/101 HP ~ 6-Cylinder
* 225/145 HP ~ 6-Cylinder
* 273/180 HP ~ 'V-8' 2-Barrel