I'm working on my 67 Impala & did that just a few days ago. My hinges were off the car. I clamped 1 of the spring ends in a vise, then bent the spring in 1 direction, inserted a washer, bent it in the other direction, inserted a washer and kept doing that until I got the spring stretched out enough to fit the hinge. Then with a pair of pliers I just started removing the washers. It worked.
You put the black end over the hood hinge top and slide the spring up and over along the steel rod that forms the handle of the brake plier tool. It is how you install the brake return spring if you have drum brakes.