66 Dart rear

Welcome new guy. A body 8 3/4 housings are few and far between.BUT they do show up here.For a complete drum to drum look to pay $1000 or more. Your 66 it's a bolt in with the right shock/u bolt plates.,,and your drive shaft will need shortened 1 1/2 to 3 inches but measure to be sure.Unless you score a shaft with the housing.
The other option would be a A body 8 1/4 from the 73 to 76's. Bolts in the same,drive shaft still needs shortened. They hold up well unless you have big HP. Go on over to the welcome wagon forum and say hey !