When you have the carburetor number (stamped on a tag, attached to the top of the carburetor), then that is golden. Match that with what we have in our carburetor kit listing and you are good to go, otherwise you have to use the best guess method.
The 4 Jet carburetor was manufactured with an identification tag attached to one of the float bowl screws on top. Some of the 4 Jets had 4 digits stamped on the top in one corner. Add 700 to the front of this number and you have the carburetor number. There were generally on pre 1956 carburetors.