kpjb,
You are right in saying that Geagua Lake's corkscrew was one of the stock models, but CP's Corkscrew is not. Silverwood, Knotts, BG Tampa, MA, and a few others have (had) the basic Corkscrew model. CP and Valleyfair's corkscrews are a slight variation upon these (with a vertical loop and some hills / helixes added).