The goal is to bring the gasoline temperature down. Easy on the 346, harder on the 355b.
The 355B intake is mated to the exhaust headers, and in the middle of it, with hot air blowing from the fan right into the carb and filter as a bonus.
The 355B carb has a very long neck so that hot air from the fan and engine bay will heat it up over time.
Gasoline in the early 30's must have been very heavy stuff to require such a setup.
My 1932 car engine did stop a few times in traffic, at low RPM so I had to take some drastic measures to avoid blocking everyone for the next 30 minutes. I could smell the gasoline before the engine would quit.
Here is what I did:
1) draw cool air from the bottom - this had by far the greatest impact on reducing percolation
2) wrap the fuel lines, fuel pump and carb in heat reflecting material.
3) Place a phenolic spacer between the carb and intake - not much space in there but every step helps
Also, another thing to keep in mind: high octane gasoline does boil at lower temp than low octane, and winter/summer gasoline formulation does change quite a bit; my problems were worse in winter (lighter gasoline).
Here are the photos for the 355Bhttp://cadillac.gs/1932engine/
For the 346, just wrap the header behind the carb and the fuel line from the pump to the carb, maybe the pump as well. That should be sufficient as the percolation is not that big of an issue on these engines. The intake is separated from the exhaust and the carb neck is short.
The original metal air filter is also a way to gather heat, beside poor air filtration I use the K&N filters in all my cars, they have so many shapes which fits any car.http://cadillac.gs/1947engine/engine-left1.JPG