I numbered the screws in the image for reference:
1: Pivot point for upper arm. Position this inward/outward to change the lever ratio and thus tension.
2: Removed this screw which held the arm in fixed position.
3: Travel stop in case the wire snaps. The arm is normally about 1/4" above this.
4: Spring attachment to upper arm. Predrill to avoid splitting the end-grain!
5: Spring attachment to brace. Choose this location to set the tension.
6 and 7: Fixed mounting for lower arm.