I noticed another important detail in the factory photo of the Z28 engine in Post #10: the valve cover retainers are UNDER the spark plug wire retainers, and the latter were installed with the "hollow" side facing down.
I've heard arguments that the spark plug wire retainers should be installed with the hollow side facing up and the valve cover retainers should be on top...inside the hollow side of the plug retainers. This factory photo shows what left the factory. Also, the picture in the 68 AIM (I don't have the AIM with me as I write this comment) on radio ground straps looks to me like a retainer order similar to what is shown in this photo. The ground strap goes between the valve cover and valve cover retainer, with the plug wire retainer on top (hollow side facing down).