Steering All Over the Place at 55mph+

Buy a 68-72 K-member and get rid of that unsafe 67 Idler arm. Grab a PST rubber style rebuild kit for 68-72 year . You will need to use a 73 and newer upper ball joints, Your car has 73 a-body upper control arms unless they used adapters on the early style small ball joints. E-body and B-body will not fit the car. Who knows maybe they didn't use the adapters and the ball joints are wobbling it the spindles. Needless to say I would fix it before you crash it.