Y'all are leading him astray. That tap on the № 6 runner is exactly where the power brake vacuum hose is supposed to go. That's where it went on every single vehicle ever made with a Slant-6 engine and power brakes. There is no port on the carburetor that can supply adequate vacuum to evacuate the booster's front compartment quickly enough—this is a safety issue, so @JimMac, do not move the brake booster hose to the carburetor or anywhere else.
You have a vacuum leak when you apply the brakes. That's because you have a faulty brake booster—its diaphragm has ruptured and/or one or more of its internal seals has failed. The type of booster you're using, which appears to be a '73-'75 A-body item, is somewhat notorious for not liking to be stored for long periods of time, whether under the hood of the car or on a shelf somewhere.
Skip the poor-quality "remanufactured" garbage you might still be able to find at parts stores or on RockAuto. Get in touch with Booster Dewey for a properly-rebuilt booster.
