What are you trying to accomplish?
If you do buy a new manifold:
You will reduce the engine weight a liitle bit, gain a little bit of horsepower and make the top of the motor look better. But don't expect to feel much in the seat of your pants if you only change the manifold. You want to be sure to select a manifold that will work with your engine combination. Meaning, don't get a single plane unit, if the motor is stock and you don't have immediate plans to change out the cam, heads and exhaust. Also, dont' buy a high rpm dual plane, if your motor isn't capable of running higher than stock rpm's. You don't have to get a new carburator, unless you want to. It's not mandatory, but it could help to increase the overall HP of the motor a little bit.
If you did add a new carb:
You could buy an aftermarket unit and gain a little horsepower, if you set it up right and you will also further improve the looks of the engine. Again, don't expect the motor to act a lot different. You will probably notice the difference in performance as well as in your wallet and gas mileage.
You really need to figure out what you are trying to accomplish now and in the future. If you plan to rebuild the motor in the future and put in some higher performance pieces, then I would wait until that time to replace those components. If that is not an option, then I would only buy pieces that would work with the current motor. They will be for lower performance applications, less expensive and probably work the best on your motor.
Example: If my motor were basically stock, I might buy an Edelbrock Performer dual plane intake, not the RPM unit, which costs more and is not necessary for a basically stock motor. I would also buy a Holley 600 CFM carb with vacuum secondaries, electric choke and the necessary vacuum ports.
If you want to buy these two parts, call Edlebrock and Holley, talk to their techs, give them your motor specs and see what they recommend. That's what they get paid to do.
Hope this helps. Just my 2 pennies worth of opinion.
