The vent only allows air into the cabin in the manner you've described. Sometimes referred to as "turning on the air conditioning"
The vents at the top of the dash aren't connected to anything. You had to purchase one of the accessory heater and demister packages to make these functional. The demister had hoses running up to these vents, which were attached to a device a bit like a miniature metal vacuum cleaner head, that fed the air up the vent.
I believe that FB/EK had a heater element accessory that fitted into the vent, but it doesn't fit the FE/FC. The plenum chamber is completely different and so is the vent itself.
Original heaters come up on Ebay and elsewhere from time to time. If you're not concerned about originality there are plenty of options out there, from small hot-rod air-cond/heater kits to anything you care to pull out of a different model car.
Hope that helps
RET