My power brakes don't feel like I'm getting any of the power assist?

On my '67 Firebird I put a front disc conversion kit on it. The kit came with everything including the booster and master cylinder. I've bled the brakes but as I'm trying to stop the pedal feels stiff and I have to press it down all the way and it feels like I'm only getting 20% of my stopping power, it stops the car but with more work than it should. On the distribution block there are two lines connecting to the master cylinder, two running to bother front wheels, and 1 running towards the rear. But here is the confusing part..there is another female threaded hole on the dis. block that has nothing connecting to it. I don't know what goes there or if that is my problem. Also I rebuilt the motor and it has a bigger than stock cam that is a .470 lift with a 320 duration and an Edelbrock thunder seriers carb. I am getting vacuum(when i unplug the line from the booster it hisses) but i'm not sure if i'm getting enough. I don't have a gauge to check it. Sorry if reading this gave you a headache I'm stressed about this.