2 barrel kickdown linkage isn’t the issue. A 2 barrel linkage works just as well as a 4 barrel linkage. If you add an extension made from all thread. As I suggested earlier. That’s your problem. That and your springs are entirely too heavy. You need to buy actual carburetor return springs. They are universal and many are available on ebay, etc. The bolt you added to the yoke slot screws up the travel of the kickdown linkage as well. In that position the kickdown linkage travel is not set up correctly. If you add an extension as I suggested. It will correct the travel of the kickdown linkage. The way you have it set up wth that bolt. It’s engaging entirely too soon. That effects the correct pump pressures shifting from one gear to the next. Kickdown as well. Ditch that bolt.