That is a heat tube for carburetors that have a heat stove to open and close the choke. A metallic tube is connected from the header heat tube to the carburetor heat stove on the choke.
I recently connected the hot air choke on my Fairlane. It has a addon plate that suppliese hot air, no fresh air supply. For the tubing I swiped a balance tube from a T-Bird steering rack & pinion(connects between R & L boots). For better efficiency, factory covered tubing with fiberglass(or maybe asbestos ) to reduce heat loss. I used a old oven door gasket on mine.
