Well, your valve springs breaking part of the story made me realize other people had that problem also. I ordered my Z28 in the spring of 1973. Within a few weeks it broke a valve spring. I went to the dealer and bought a new spring and installed it. About a month later, it broke another one. I figured I was about to run out of luck and a dropped valve was coming. So I went to the dealer and ordered a full set. When I replaced them, I discovered that the springs had a color stripe painted down their sides. I had 3 silver ones, 4 brown ones and the rest were purple. (The two that had broke were silver.) The new ones were all purple. I think the factory color codes them as to what cam/engine they should be used on and the person that put my heads together was just using whatever was handy!