Before you think about boosters, have you determined what pedal ratio you have? It maybe easier to alter this than fit additional hardware. I like a 6:1 or a 7:1 pedal ratio without using a booster/servo.
Boosters are usually used for discs because of the higher pressures needed and they lessen the driver effort needed to operate discs brakes.
Another thing to consider is high lift cams can cause the booster to run out of vacuum at tickover (especially in traffic when you need your brakes!!), the smaller boosters (the 7" under the floor types) are very prone to this.
I guess you have 40 ford brakes with buick drums that are the non energising type? Are the linings adjusted ok?
Mel