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.
The funny thing about science is that if you change one miniscule parameter you change the entire outcome to the way you want it.
