74 Dart Stalls when in gear.

Cheers: I am having trouble with my Dart.Aluminum intake , 600 Holley 4 barrel ,Billet distributor ,MSD Box , Super 2 Coil ,MSD Wires , 292-508 lift cam. Engine was rebuilt at one point and pulls strong but I don't know the internal Specs.

Problem:
It won't stay running in Drive or reverse. Even if I crank the idle up. It will try to stall just by pushing on the brakes. It stalls immediately when I put it in gear. I have a back up Booster which I'm going to try but I want to know how ineffective the brakes will be if I disconnect the booster and plug the vacuum line for test purposes. I don't want to go flying through my Garage wall or backwards into my Scamp. The Carb is a Holley 600 and I was also wondering if it should have some mechanism to "Boost" the idle when in gear. This Holley has been somewhat butchered as the Choke and various other things have been eliminated from the equation. Please steer me in the right direction. I am not really a carburetor guy and worked for years only on FI Hondas. Thanks in advance and Please Help.