There is a tube that connects in to the manifold from the 2100-D v-2 carburetor. The tube is connected to the carburetor with a short piece of vacuum tubing. According to my Ford shop manual, which I purchased when I bought the truck new, it connects to the choke clean air tube on the carburetor. The end that goes into the manifold is rusted off.

 

Maybe if you posted in the correct forum, you would get more results.