Ed - Buick offered a factory 2 x 2 set-up in 1941 and 1942. They actually used progressive linkage! Many (most?) were removed during WWII due to gas rationing.
For decades, we have been helping Buick owners replace the the primary/secondary carbs with two "normal" carbs for those that drive their cars. Smoother performance, and somewhat better fuel economy.
There are generally a couple of threads running at any time on the Buick section of the AACA forums. The Buick folks are pretty active.
As far as I am aware, this set-up is the only factory multiple carb set-up on an inline engine with progressive linkage.
Jon.
