I have a set of springs i pulled off a 69 convertible, will likely break the stacks down and add a leaf to my dart. And maybe one to barracuda as well. The suspension has been out of both cars so it will be an easy job.
I've seen a lot of reviews and people posting about the 35 dollar add a leaf kit from summit. Most people seem to like them, but I also was reading adding a leaf is quite a bit more work.