In 1957, Pontiac used both the Rochester 4-GC and the Carter AFB. For reasons I won't discuss in this thread, the Carter is MUCH HIGHER priced. However, the Rochester is an EXCELLENT four barrel. If you want a four barrel, find a used one and manifold, and rebuild the 4-GC.
A Rochester 2-GC from a Pontiac 370 or 389 might be another option, but the four barrel with the small primaries would be easier to tune to the 347 than would the two barrel.
The Stromberg two barrel type WW carburetors are excellent carburetors, but very scarce and difficult to locate for the GMC engine.
The four barrel should give a modest increase in performance (power, driveability, AND economy); but not as much as if you also changed other components of the engine (cam, compression, exhaust, etc.).
Jon.
