Still putting my 312 back together for my  '57 Bird. Running the factory E dual quads. In the past I had totally blocked the heat passage with a thin piece of stainless steel. Plus side was that carbs did not boil over as much.  Down side was no choke but don't drive it much in cold weather and never was a problem. Debating on not blocking it and using the chokes. Any pros or cons to either option that I have not mentioned?