Typically the large one at the base of the carb in the rear is used for brake booster. There may be a small one near the base on the front side, and another one, a little larger, near the base of the carb in front. The larger one in front is for the PCV. The small one can be T'ed for vacuum advance and trans.
The engine in the pic has a port threaded into the manifold. You can use that for vacuum advance, trans, brake booster as well and cap the ports on the carb.
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Hank
70 Chevelle SS396(454), M20, 3.73
My Chevelle
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12-17-2012, 02:58 PM
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