The carburetor on 235 truck engines on Hydra-Matic-equipped trucks came with an automatic choke, using the tube and manifold stove as was used on car 235 engines.

In this photo, you can see the tube and almost see the stove.

As Wrenchbender Ret. confirmed, the tube goes into a hole in the stove and is warmed by the heat coming from the manifold - from the warmed air and by contact with the warmed/hot stove.

Tim