Brake Booster - Replace?

Yesterday evening I was able to get my '69 Fairlane 500 running pretty good...in fact, it was idling along real well and I decided to take it for a spin around the block. I first began testing the brakes and everything in the alley, and the brakes are just very week. The pedal feels like it only moves about 2 inches and it's not a 'good pedal' that we all like.

There is plenty of brake fluid in the reservoir, I suspect that booster just needs replaced, but I'm not sure. I believe these work off vaccum, so I'd first like to know what I should check before replacement. Is there anything I could do to improve braking prior to replacing the booster?

Any ideas?

Through Google, I did find a bit more info on vaccum boosters:

To check the vacuum booster, pump the brake pedal with the engine off until you've bled off all the vacuum from the unit. Then hold the pedal down and start the engine. You should feel the pedal depress slightly as engine vacuum enters the booster and pulls on the diaphragm. No change? Then check the vacuum hose connection and engine vacuum. If okay, the problem is in the booster and the booster needs to be replaced.
Vacuum boosters also have an external one-way check valve at the hose inlet that closes when the engine is either shut off or stalls. This traps vacuum inside the booster so it can still provide one or two power assisted stops until the engine is restarted. The valve also helps maintain vacuum when intake vacuum is low (when the engine is under load or is running at wide open throttle). You can check the valve by removing it and trying to blow through it from both sides. It should pass air from the rear but not from the front.