If you notice in the dark area of your
intake manifold under the
carburetor, there is a hole. That hole is where that elbow mounts. it does not have to fit tight, as there is no problem if there is a little seepage. This is the exhaust cross over are of the
intake manifold. There is a tube in there that probably should be replaced if you are getting any exhaust gas coming from that area. They last a long time, so you should get 20-25 years out of the tube if your replace it. They used to sell for about 10-12 bucks but they are closer to 20 now. If it were my car, I would remove the
intake manifold, knock the tube out and put a new one and a new mushroom on the other side of the manifold. The tube, mushroom and a set of gaskets will run you in the $50-60 range and will solve the problem of the tube leaking exhaust, which will damage the choke mechanism.
Here is how it works, There is a heat riser valve located on the left side of the engine between the exhaust manifold and the header pipe of the exhaust system. The valve is operated by a bimetal spring that keeps the valve closed when the engine is cold. This then forces the exhaust to flow through the
intake manifold, under the
carburetor to warm the
carburetor to allow the gasoline to vaporize better. There is a tube that goes through that passage and when installed correctly, it seals any exhaust leak. There is a slight vacuum provided by the
carburetor that draws air up into the choke area. The elbow in your photo is supposed to attach to the pipe in the manifold and it then draws air into the choke to warm it. Once the engine warms up, the heat riser will open and most of the exhaust will then flow out through the exhaust pipes and no longer through that passage way. There is always some that is in there, but at a much lesser extent than when the valve is closed. If you bring the system back to factory spec, you will have a much better running car, especially when cold.
When you buy the intake gaskets, get the ones for the truck engine, as they have just a small hole in the crossover area and will not darken your engine paint on the manifold as much.