Correction, grasshoppah. I *attempted* this.
I tried to fit a 4150/4160 type Holley (four barrel/center hung bowls) *centered* over the 12A manifold. There is negative clearance with the water pump housing. No go. I have *heard* of people making it fit in a similar way by offsetting the carb rearwards, but I worry about how well that'd work in regards to differing airflow/mixture quality to the front rotor vs. the rear rotor. Would take more fangling than it's worth IMO, for about the same amount of work to make it "right" you could just dig out the MIG welder and fabricate a tunnel-ram type intake manifold that hangs the carb further outboard, or further up. Or just get a RB intake manifold and cut out the runner dividers for the first half inch or so from the carb surface so that the vacuum signals to the carb circuits (the pulsing airflow from each rotor) is weakened and smoothed out, which is what the Holley expects to see, so it won't require hardcore recalibration.
Bleh. Anywhich, that's about it.