I had to do one on mine a while ago. If I remember correctly, I placed the spring over the rear ear of the hinge, then used a t bar that had a hook on it to pull the spring and I slid the spring over the front bolt/anchor. Mine are off now and torn apart so I can't run out there and look at it either.

I've also seen where guys would take the spring, bend it with your hands and stick washers in between the springs and repete the process on both sides until you get the length you need to install the spring. Then remove the washers.