Question about a cars's seat rails.

This might sound stupid, but does anyone know or know of a chart or something with the width's of different car's seats and rails. I'm doing a project and am building a base for the seat out of a 2001 Mercury Cougar (http://shop.ebay.com/i.html?_nkw=mercury+cougar), and I need to know how wide the base should be for the rails under the seat to mount correctly. I didn't know if it was the same as the Puma or not.