The comments above are great, but need clarification. "Park" consists of two separate functions and linkages.
1. "Transmission gear selector", which is a series of levers in your car. This controls the transmission shifts thru the "valve body". The factory or Haynes manual should explain how to adjust the linkage, since that is a regular maintenance item. Similar even in new cars. If not adjusted correct, the "neutral safety" switch will be open which disables the starter relay.
2. The other is the "park sprag lock" which is a cable going to the rear of the transmission. This is a cable in all Dart years. This sets a pawl in a tooth on the output shaft and locks the wheels. In newer Chryslers this is done in #1 via an internal linkage in the tranny. This one is most important for safety since not everyone (ex. my wife) thinks to set the "parking brake" (or "E-brake"). My friend's truck was recently messed up by his wife not setting the brake and leaving in "D".
