All of my 63 carburetors had the chimney and all my 62’s do not have it. I am only assuming that they have not been changed in the past.
On another note, I finely check my MPG since I made the jet modifications and puled out the needle. I am at 17 MPG where before, I “think” I was at 19. I am going to make another change on this and see if I can split the difference.