What is this steering wheel?

You have a 68-70 A or B-body sport wheel, your car would have had the Tuff Wheel as an optional sport wheel. If you want to keep it in the car you can find a pad from a 69 Barracuda or Dart (swap to Plymouth emblem). If not, you should be able to trade your wheel for a correct one. I wish I had one to trade ya because that would look nicer than the worn one in my 69 GTS convert. JB