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

I've always been more of an E-body guy. Like the 67-69 Barracudas too. Got all the different trim levels and what came with what on those cars covered. 67-69 Darts? Not so much. So, I'm going to come clean and fess up that I don't really know the differences between the Dart, Dart GT and the Dart GTS trim levels on the 67-69 Darts. So, with that said, can you A-body experts school me on learning the differences between the different trim levels? Or maybe point me to an online reference where I can school myself? Got an interesting Dart here in my area and I want to get schooled up on what I'm looking at before I head over there to take a look at it. Thanks in advance for your help.