The metering rods on the Carter AFB are stepped and effectively open the gas flow more when you step on the gas and close down when cruising. Most other carbs have replaceable jets of differing sizes to give you EITHER more performance OR better mileage; both within limits, of course. The Edelbrock carb looks almost identical to the AFB, uses the same type metering rods, etc. In fact, I wouldn't be at all surprised to find that Edelbrock had Magneti-Marelli Powertrain USA, Inc., re-manufacture AFB's or reverse engineer them. One difference is the Edelbrock is all aluminum; the AFB used a phenolic middle section to keep the fuel cool(er?), thus helping maintain consistent operation at widely varying under-hood temperatures. Personally, I'd choose the AFB over the Edelbrock strictly on price, and stay away from the venerable Holley double-pumper unless you enjoy pumping lots of gas into your tank. That said, just going to a larger c.f.m. carb. won't necessarily give you a performance boost; the manifold has to be able to 'flow' the gas/air mixture properly. Now you're talking about a new manifold with equal-length runners and more money - and it may not fit inside your doghouse! Measure carefully to make sure you have the necessary clearance.
Lastly, switching from a carb to e.f.i. is neither easy nor cheap. Lots more hardware additions and/or changes, which may include a 'performance tuner' just to get it running smoothly, and a BIG, BIG wiring job. You'd probably be better off swapping out the entire engine for one already set up for e.f.i.
