If you're looking to gain performance with multiple carbs, and not just going for the eye candy, you do have to consider the entire package. That includes selecting an appropriate camshaft as well as improving the exhaust system to allow the engine to take advantage of the intake setup. You'll also want to consider improvements to the ignition system.
This is very good advise and those who ignore it wind up with the dreaded bog, bad mileage, and manifolds on ebay. Engine building is much like baking a cake...too much or too little of any one ingredient can ruin the outcome.
Personally I think a hokey linkage adjusted by bending is a big culprit for poor results as the carbs are simply not actuated simultaneously.
