A body buyers guide??
Dusters/Demon/Dart Sport are usually lighter than the Dart/Scamp
67-69 2 Door post cars are lightest IIRC.
67 has a one year only steering gear assembly, Idler arm. Look for a 68+ car or swap the K frame to a later piece if you find a nice 67.
73+ cars started to pork up on weight.
I have some cars for sale, They are in CA. If you search post started by me in my profile, you'll find a couple, 71 Dart, 73 Dart Sport.