Not Webers, but the idea is the same.
I'v been playing with mine over the years, trying to get it just right. I finally scrapped the original design, and made my own. But, here's what I learned. It is critical that all blades oepn exactly the same amount at exactly the same time. This is critical to smooth operation and power production. Even the slightest differance will affect performance. Before tuning the carbs, you have to get the balance exactly right from idle to WOT.
The central bell crank is on a pedestal, bolted to the boss in the manifold. I made the pedestal out of some 2" alum hex rod. Very stable, no flex at all.
The arms I made from 3/8" hex rod. I decided to make my own because I didn't have a local source for them. I didn't want to try one length, throw it away, and wait a week for the next size to arrive. I got it all done in 2 days. The only tools I had to buy was a left handed tap. So I'm sure I saved some money.
I use a throttle cable. It's easy to route, and no real fabrication involved. It doesn't look original, but I don't care about that. I had to make the cable bracket you can see in the second picture. Not a big deal. I made it out of some sheet metal I had lying around. Took some experimentation to get it where I wanted it.
I must have spent a week working on the linkage. But now it's perfect, works smooth, and the balance is perfect throughout the range. And, I made it myself.