Without having all the various springs Chevrolet used on '69 Camaros, it's impossible for me to know how they adjusted spring rate and loaded height for each car weight. your coil wire is a bit thicker than I measured (assuming we both measured correctly and consistently), thus your spring would be for a heavier weight car. As you see from the 69 Camaro Usage Chart, there were a lot of different springs, for the multitude of engines they offered in the camaro. http://www.camaros.org/images/pages/chassis/69_spring_ID_PA34.jpg
For the Z28, only the following springs were used depending on the additional front end weights for your optional items:12437 302 Eng. Z28)
69 -148 EY
Over 148 YH
My car's options totaled between 76 and 107 lbs (from the factory) where the EY spring would be correct, and that was what the original springs were labeled. If your spring coil wire dia is thicker then it may be the YH spring (for the heaviest of addon weight ranges). You can check the weight charts to see what options might have added up to the 148 lbs (Plus) to justify the YH spring? From the charts, it seems it would require a Z28 to have almost ALL the possible options to reach the YH level of spring, certainly it appears the tape player would be required,and that's a rare option.