Couple of things come to mind on the surging issue. first, you have to have heat to the manifold. Putting water heat to my manifold all those many years ago was an enormous improvement. Second, you might consider switching to the smaller 216 Rochester B carbs. Smaller carbs, better for drivability. Lastly, you have to synch the cabs in with a Unisyn or similar tool. Both carbs have to have the throttle blades adjusted the same at idle, in essence, in a perfect world, the blades occupy the same relative position to the off idle transition slot or hole, as the other. Otherwise, one carb will lead the other into the off idle circuit and give you the sort of surging/stumble you describe. The Unisyn uses vacuum through the too and carb to help dial in the adjustment.
