There probably is not a "one answer for all"; but in general properly SIZED AND TUNED multiple carbs will be marginally better than a properly sized and tuned single carb due to better fuel distribution to all cylinders.
So how much is "marginally better"??? Lets say that the "perfect" multiple carb setup is 100 percent; then the "perfect" single carb setup will probably be at 96~98 percent. So while measurable on a dynomometer, can you measure 2 percent HP increase by the "seat of the pants"? Can you measure a 2 percent increase in fuel economy?
The key in all of the above is properly sized and tuned.
As to whether 2 or 3 or 5 or ??? carburetors??? Much depends on head design (individual ports, siamesed ports, triple ports, etc.) and whether the carbs will be run simultaneously or progressive. I personally am a firm believer that the number of "barrels" should be an even divisor of the number of cylinders; so for a six-cylinder engine, that means 1, 2, 3, or 6 1-barrel carburetors; or maybe 1 or 3 two-barrel carburetors. A single four-barrel with primaries and secondaries feeding a common plenum is also a possibility.
The theory AND practice remain the same, regardless of the displacement, assuming that carburetors of sufficient size may be obtained.
Again, and it cannot be over-stated: the initial selection of the carburetors, and tuning on the engine is the key.
Jon.
