The early kickdown links and arms the 340 used had adjustments on both top and bottom, the later ones just have the bottom adjustment but work so you have a typical later setup.
Luckily I found a early 340 setup for the Dart and it's nice, I have used a reworked 2bbl setup and the later one similar to yours and all of them can work if your willing to tweak and adjust as needed.
I had to make the 2bbl setup think it was longer by cheating with a small bolt in the kickdown spring slide area up top seeing how it was very hard to find the proper A body kickdown linkage even back in the early 80's when I decided to upgrade the intake/carb setup.