OK, too doggone cold to work, so I dug through more boxes. I WAS out of 2100 carbs that I knew where were. One of these days will find ALL my carbs (yeah, right!).
The cleaner of the two is an early production 2100s (no exact date code).
The grungier of the two is a late production 2100s produced in April of 1956.
In the other two pictures, it is apparent that the hole in the throttle arm when closed is approximately 4 o'clock (using "up" as a 12 o'clock reference), and is located at approximately 2 o'clock when the throttle is open. This agrees with the OP's comments about the Rochester.
And no, without scanning an aperature card, I don't know all differences that exist between the early and later production, other than the obvious change to the stamping of the part number. The tech sheet does specify that the position of the vacuum port was moved by 0.005 inch, and the pump discharge valve was changed from the ball and weight, to a pointed weight without the ball.
Jon
Jon, FYI- Mine has the exact 2100 stamp as the late production(dirty one).
