Again, Langdon's Stovebolt website shows the adaptors. And, yes you need one as your Webber is a four bolt and your bolting to a two bolt manifold. There are several other online parts houses that handle all the pieces you'll need like air cleaner, jets etc etc. Here's a Webber store, www.piercemanifolds.com
Best of luck


Jim, I.I. #173
(It's easier to get forgiveness than permission!)