Well, I'm a poor one to answer your questions because I've never worked on this specific carburetor. But the attached excerpt from the parts book shows a gasket between the needle valve seat and the carburetor bowl (item #34).
If it's anything like other needle valve seat gaskets, I wouldn't recommend trying to make one, but would buy one from one of the usual suppliers, such as Robert's Carburetor Repair. (Theirs lists for $0.57.)
However, before one assumes the gasket is the culprit, check the needle and seat itself to ensure they seal properly - and check to ensure the carburetor bowl is not cracked or has some deficiency that might let fuel pass through from the needle zone into the bowl itself. There can be lots of nasty little gremlins that might be the cause of fuel overflowing the bowl, and only a keen eye and a detective's mindset can find them.