What type of dart do I have?

Agree....and we should be on the positive and not on the beat down. Without reguard to the missing fender tag - it is a GT with a 4sp and a 8 3/4 which should indicate it was once a 4 pot......lots of years and countries between 1966.

Show a picture of the rear under the bumper left side and by chance the left side might be orginal with a tell tale sign.
Two barrel four speed A-bodies from the factory are rare, but they are out there. Also no cutout on '66 or '67 Darts for the big resonator tip.