I have one that was rebuilt 25 years ago and is packaged up ready to go.
It was out of a 65 4-door b-body with a 4-speed and 8.75 rear.
What length do you need.
You could shorten it to fit what you need.
do not have the 8.75 in the dart yet.. so I don't have any measurements yet. but .......... If your DS came out of a 65 bbody, it will be a few inches longer Right ?