Besides the '74 factory rig, I've been told the early '71s also had a fresh air inlet. Both these were behind the glove box, feeding the heater/ac boxe from a flex hose. But the vast majority of narrow-body Panteras had none. Kind of difficult to describe the factory assembly and they both take different actuation levers on the console to work.
I was fighting the factory AC at the time so I added vents to our '72-1/2 by carefully measuring, then drilling two big holes in the cowl opening under the removable wiper grilles. You can barely fit a 2-1/2" hole saw thru the vent openings. I used large brass 90 degree sweat-solder fittings of the same size in the holes. The fittings are oriented so they point back at the seats, slightly raised from the cowl bottom so rainwater can't flow in, with 'custom' water baffles on top. These are made of trimmed aluminum beer cans with a big wide slot halfway around the top for air in, sitting on top of the brass fittings & held in place only by the factory wiper grilles that snap in place. No water has entered the car since I did this in the late '80s.
Silicone seals the fittings to the steel cowl and the beer can intakes to the fitting tops. The open ends in the cabin have home-made aluminum throttle blades with little levers and push/pull-rods to open/close the vents separately. One is almost in-line with the driver's left leg, the other is right next to the heater/ac box on the passenger's left. While the openings are not very large, considerable fresh air does flow into the car; more the faster you go. In cold weather, the shut-off valves are necessary! I wrote this up in the POCA Newsletter at the time, and the home-made rig has given some ventilation and no trouble since adding them. Downloads of ALL archived Newsletters are available on POCA's web site.