Super Six Linkage
This is going to sound funny but I had a 2bbl slant six a couple of years ago with a modified 1 bbl kickdown linkage on it. I bought the correct linkage (that you are looking for) on Ebay and put it in my garage.
To keep this story short, I wont get into why I never installed it, but i didn't and it is here somewhere. If fact I have about 6 regular 1bbl kickdown linkages and I can't identify which one is the rare 2 bbl setup.
If someone could post pics of the differences I MIGHT be able to find the correct one for you.
Good Luck!