The brake booster taps it's vacuum source from the carburetor. On a stock Rochester Quadrajet , there will be a tapped 3/8" NPT port - down low on the back. Here are some pictures. The ones that show the hole plugged off are of a truck equipped with hydro-boost brakes:
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On any Q-jet - I have ever seen - the scavenging port for the PCV hose is directly under the filter housing:
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That port is labeled "J" (IIRC), and it is noticeably bigger than all the other ports.