I know neither Yakima Racks nor Thule Racks make a 1997 Ford Crown Victoria roof rack that will mount on non-permanently as they do for most other car models. What you cna do though is permanently install a car rack on top by using a set of four Yakima #7 Landing Pads. These are made to permanently install onto vehicles with metal roofs. Once the #7 Landing Pads are in place you then connect a set of four Yakima Control Towers to the Landing Pads. Then all you do is attach a pair of yakima cross bars (get the 58 inch length bars for the Ford Crown Victoria) to the Control Towers and you have a very solid base rack foundation that you can then connect any of yakima racks gear carriers to the pair of cross bars. You could also check out this
list of Ford car rack pictures or these
Ford rack photos for other possible solutions.