I'm running a 545 with an Edlebrock dual-plane Air Gap. I've been thinking of grinding most of the wall between the two plenums - at least to the floor of the upper plenum for a little more performance. At this time I don't want to go to a single-plane manifold. I have this engine in a '79 F350 that I pull a fifth wheel trailer and I feel that the dual-plane gives me a little more lower end torque and I'm not looking for power up high.
I have a spacer and found out at the machine shop that I use that I can notch & blend the parts of the spacer that separates the 4 carb openings - it's not an open plenum spacer. It should be easier than cutting on the intake.