So he's got the RPM manifold and it's on the car - why remove it? It takes some work on a stock manifold to equal the out-of-the-box performance of the RPM manifold.
The Holley is a little easier to tune than an AFB, but the AFB is still straight forward and much easier than a Quadrajet to set up properly. People bad mouth AFB's on here, but isn't it surprising how well AFB's all of a sudden work when placed on a 2-4 manifold? How many people bad mouth the AFB and have never owned one? I've had them on many of my cars from the mid 50's on up, and they have proven to be the most trouble free of all the carbs out there. I currently run Holley's, AFB's and Quadrajet's so I'm not predisposed to any single make of carb, and I work on all of them. AFB's just keep on running, Holley's have some trouble with dirt, and the hundreds of varieties of Quadrajets takes someone like Cliff to keep track of them all.
An engine is nothing more than an air pump, and the carburetor is blind to what it is sitting on. How many people set the spring on the secondary air flap to exactly one turn and never think another thing about it? That is no different than Carter selecting the weight on their secondary air flap. In either case, you better have a really sensitive butt to feel any slight difference in opening rate. There is a thin margin of opening rates on the air flaps that work satisfactory, and most people are better off not playing with the factory adjustments.
jwcfbd, is the rich condition at idle, part throttle, or full throttle?