'67 Dart with '68 idler arm?

I have never seen one like that for a 67. Looks like someone adapted a 68. the 68 /later, maybe you are aware, has a bracket under the arm through which the bolt goes. In other words the arm is sandwiched between the top and bottom brackets.

You can modify the 67 K to take a 68 /later arm, but it would be some work.