Idler arm, worse set-up on a 67 as it doesn't sandwich between two pieces of metal, a through bolt holds it on at one side. I had it once in my 69 Dart 383 and it was the idler arm. Even if you have a new one on it there still could be issues with it especially with parts made today.
All it takes is a few scraps of metal and a welder to correct that. Did it on both of the 66-67 I used to own.
