i don't have a set of stock Z28 springs, but i have a set of the Eibach springs that were sold through SLP for the "performance" suspension option with the WS6's and SS's. they're the stock springs on my SS. they are on my car still, but i have a set of eibach pro-kit springs waiting to go on. They are rated at like .75" of drop or something like that. If this is something you might be interested in, i can make it a point to swap them out sometime this week?
oh my car has like 54k miles on it if that means anything in terms of spring wear maybe i have no idea?