Depending on your mechanical inclination, you can learn how to diagnose & fix what you've got, or be doomed to buying parts until eternity comes to fix things.
You have hit on something with power brake problem. You obviously have a vacuum leak somewhere. This will really screw up the way any engine runs with any kind of carb. What kind of intake do you have that Holley sitting on? It maybe be leaking between the intake and carb. Find that leak! As a tip, Holley's have power valves which are notorious for causing problems when they get old or have the wrong vacuum level installed which causes real bad driveability.
Here is quicky article on a Holley 1850 rebuild. web page
