What is the mushroom cap on the intake below the left rear carb mounting stud?  It looks like it is some kind of breather as it has holes on the inside of the cap.  Mine has a little rust and I'm wondering if I should replace it with something.

John, I think someone will come along with much more expertise than me, but it might be the end of the choke heat tube. If I am correct, the tube that breather is hooked to goes from one side of the intake to the other side (routed under the carb). If you look into the intake manifold openings where the carb sits, can you see a tube? These tubes sometimes burn off in the middle or anywhere in between one side of the manifold and the other side. My experience is with a four barrell intake, not a two barrell, but I would think it would be the same. If I am correct, what you do with the breather and the tube depends on what you want to do with what your going to use for a choke (manual, electric, or the stock one that runs off the heat choke tube). See if you can find the other end of the tube on the opposite side of the manifold and check to see if its routed thru the intake to the other side. If it looks like its all together, (not in burned off sections), see if you can get some air pressure from one side to the other without losing pressure in the middle. 

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's