If it's bogging down with one carburetor, opening up twice as much venturi area with a 2-carb setup is going to make it twice as sensitive to gas pedal position. Carburetors mix fuel by creating vacuum in the venturi area of the casting, and anytime you give the air more places to go, or a too-big venturi, you slow down the airflow and reduce the vacuum that's causing the fuel to flow into the airstream. The result is not enough fuel, too much air, and a flat spot. If you don't have the right gear ratio (transmission in the wrong gear, or too high a rear end ratio) the problem will be much more noticeable because you've got the engine lugged down to the point it can't accelerate. Proper carburetion is simply getting the right amount of fuel mixed with the right airflow, and doing it through the correct engine RPM range to make the vehicle perform. Any noticeable departure from how the factory engineers did it with millions of engines is introducing a whole bunch of variables into the equation that will have to be sorted out one at a time. Fortunately, most hobbyists and/or hotrodders think they're a whole lot smarter than the guys who made their living building these old trucks! Good luck!
Jerry
