The spring does not hook to the body..it rides in a slide on the left inner fender well.
The trick is to take an S hook and load tension on the spring by turning it CCW and then hooking it into a hole in the hood channel with the S hook. It is then under tension and when you put the hood back on, you release the hook and the spring will tension down into the slide recepticle.
This is for the front hinged 113 chassis/280sl hood [68-71]..the later 107 chassis/280sl does not use this system as they hinge the hood at the rear and do not require hood removal to change the radiator.