I'm looking for recommendations for some stiffer rear springs for my 1999 grand marquis. I did look at adtr.net and they have some Eaton Detroit springs. But they don't give much of a description on whether or not they are performance springs or just a direct stock replacement. Basically I'm looking for performance gains from stock, and I also want the rear of the car to sit just a little bit higher than it does currently. Any input would be appreciated.