ive been buying and selling gts darts for 20 years,if as you described with a fendertag 7k to about 9500 is a fair price they made just over a 1k 340 4spd gts cars in 1969.
I think this is more like it. A solid one with a slant auto is worth $2500 minimum in my book. Considering what it takes to upgrade one to a V8 stick, provided the drivetrain is decent I'd give at least 5k.