My 68 Darts use the plastic clip. I think the 67 year is when it was changed to the clip style. Also check to see if your cable has laid on your exhaust pipe at some point and melted. I have seen that alot. The plastic melts and when your car cools off the plastic hardens and locks the cable from spinning. That will twist off the end of the inside cable. You might check the back of your speedo, too. Usually when you take the instrument panel loose, it's tilted forward to see what is attached to it. When it's tilted forward and you are trying to get it loose, the plastic clip cracks where it is attached to the speedo cable. Then it separates leaving the clip on the back of the speedo. Sometimes super glue or JB Weld will hold it back together. I've also seen a worm clamp used.