Finding the leak ain't so bad. Go get yourself a vacuum tester kit. Same thing as those 1 person brake bleeder tools. Hook it in to the vacuum tree and see if the vacuum is low. Should pull around 16 @ idle with a stock cam. If not, start pinching off various parts of the rubber hoses leading to different things until it starts to move towards 16, then you've found the culprit system.
Don't forget that a vacuum leak doesn't necessarily have to be a vacuum line. The intake manifold gaskets are under a vacuum, and if they leak, you have a vacuum leak. Use carb cleaner or starting fluid to check the gaskets for air leaks while its running.