"Rare" is one of the most overused words when talking about old cars. Approximately 30,000 Dart GT's built in 66 and approx 1/3 were V8's. Simple Googke search.
GT was a higher trim package which got you bucket seats and console. Very similar to top of the line Valiant Signet. Same basic car as the others, just a little fancier. Reminds me of early 60's Chevy Impala SS which were just trim packages and didn't designate high performance at all.
If yours has the Charger 273 engine with sway bar, disc brakes, etc. That's as good as it got (except a 4 speed) for 66.
https://www.hemmings.com/stories/article/1965-66-dodge-dart-gt
@65dartcharger might know more
