[XJguy]

You are starting out with a car that has a fairly good aero package. Don't let its large size make you think otherwise. One thing that was implemented in later models -up to current is a new trunk lid that incorporates a bit of lip/spoiler. This was done to improve aerodynamic efficiency. An addition of some aluminum angle bar adhered to your lid, should act as a Gurney flap and bring you the same result...a clean break for passing air.

I would further enclose the rear wheels, vent all 4 wheel wells, vent the radiator through the hood. Remove any mechanical fans for electrical ones. Swap out the heavy cast iron brake components if so equipped, and substitute for light weight aluminum. Police Interceptor models have many high performance parts that may actually weigh less, being made of aluminum alloys instead of steel.

A lowered car is only more aerodynamic if it is done so in lieu of an underbody that is smooth. With a smooth underbody there is little need to lower the car (aside from handling). However you do have to compensate for the gapping holes of the wheel wells, which should be a close tight fit to the wheels. With a car that is very low you start experiencing a ground effect in which the car is sucked down into the pavement, which increases traction, but also drag....if not managed by a proper venturi and or spoiler/wing, at high speeds it can render you airborn.

If I am not mistaken behind those plastic fascias is a heavy steel bumper...that too can be nixed for nothing, or a lighter home made option, or trimmed, dont know if any year models cane with aluminum back there as so many new cars now do.