X33 & X77 are Z28, X66 is the designation for a big block. Price seems within reason. Everything has gone nuts over the past decade. Check it over real good for hidden rust or bad repairs. Make sure of what is there... glass, trim, brackets, etc. That stuff can really nickle and dime you. I think I would start somewhere around $10K - $11K and see where the negotiations go.
Here is a good break down of the cowl tag...
http://www.camaros.org/diffs69.shtml