Do you need one for a 383 or 440? They are different. The 383 version is a little taller to make up for the low deck on a 383/400.
To tell them apart. Set the base on a flat surface, if it sits flat on the air horn surface (where it mates to the carb) then it's for a 383. If it sits on the back of the air horn and the front of the hood seal portion, then it's for a 440.