I am running a Edelbrock intake manifold and carb on a 3.5 right now and am building a 3.9 that I have in the garage that will also be running the Edelbrock carb set up. The original set up was a twin carb that was lacking considerably in power, the 4 barrel made a big difference as did the intake manifold.
On the 3.9 I am going with a new cam for more torque, lifters, notched divider in the intake manifold and maybe a Holley Truck Avenger carb.
Overall I am very happy with it.