Don't think mine has it, maybe the previous owner removed it??? Since it looks like it will be located to the rear of the car and kind of hidden I will take a look underneath from the passenger side rocker panel and let you know...
Yours may look different, as the one in the photo is of a later model, but the function is still the same. You should be able to see it from the top. Grab the weight and give a twist. If it moves, then the flapper is probably functioning correctly. If it's stuck, it may be stuck in the closed position, which is no-good. If it's stuck in the open position, you're gold!
The one on my Dart, when I bought the car, was stuck closed. Made the car perform like a DOG! After I freed it up, you could feel the difference.
