The hole in the pulley plate and the bolt near the centerline should be the spring mounting points.
The easiest way to install a spring is to loop a piece of rope or nylon cord on one end of the spring and pull it over the stud.The bolt is a hex head tight against the plate. I can loosen it, maybe hook something over it to connect the spring to. When I have the belt, I can try that. That was my best guess so far. Thanks.