Some YF's had the number stamped on the razor back that runs vertical of the carburetor body.
The 1940 can have either a Holley LIST. i.e. 3450-1, or a Ford number: D2FG-AB
Some older carburetors had 4 numbers stamped on the face of the mount. Add 700 in front of the 4 numbers. i.e. 7004965. Stamped numbers on the carburetor are casting numbers, not carb numbers.