‘67 Formula S 273 balancer wheel and belt pulleys

Yep, that a/c pulley is a vibration damper in design. I don't know if the compumper operation resonated through the car or the damper just absorbed some drive belt bounce.
Everything was engineered base model back then. A single belt for alt' and water pump. The power steering pulley would be added on, then a/c pulley added on.
If you have timing cover, water pump, all this accessory and drive belt stuff on the 78 model engine, you'll notice its all quite different. Power steering is 1st belt, that pump re-positioned ( lower ). Then a matched set of belts drive alt' and a/c. Timing scale and lower water hose on opposite sides. I think all the earlier stuff will bolt onto the 78 model block. Good luck with it.