I installed power disc brakes on my 67. When I got the booster the check valve had one of the two ports broke, so I had to replace it. If the vacuum hose attaches to one port what attaches to the other? Is it left open or does it get plugged? I want to make sure I get it right.

Either plug it or it will supply other vacuum related components (i.e. a/c, tilt wheel, or speed control) But if you have a/c or tilt, you should already have the canisters to provide the extra vacuum needed. Since it was used on the Torinos, Cougars and possibly other Fords, it could be for other items.

Typically, There was a steel line and hose to the check valve. If the car had a manual trans, the extra was capped, an auto trans would have the modulator connected to the other port.