So the answer is to remove the rack and screws and drop the tank to in sure it is clear or if not, replace the tank? Is that the only issue?
I think this is the only issue and as long as the car has not been in an accident, the rack (if present) can be removed and you are good to go. No damage to the fuel tank without a massive rear impact can occur.
The cars with the basic police package are rather spartan. They come with only AM/FM radio, no cruise control, vinyl floor covering instead of carpet, and vinyl rear seats. You get dual exhaust, higher rear axle ratio (lower gears), in some cases traction lock differential, heavy duty chassis, shocks, wheels, engine cooling and a heavy duty transmission.
I have seen almost new police package Crown Victorias on eBay that were ordered with other desirable options such as full capeting, CD player, cruise control, full body side moulding, cloth rear seats, etc. Apparently these are cars ordered for detectives or police chiefs, in some cases for FBI/CIA. They are just like a regular passenger Crown Victoria, except with heavy duty components. Especially the heavy duty transmission is something that you cannot get on a regular Crown Victoria.
There was a 2008 police package Crown Victoria with those nice options on eBay recently for something like $ 23k with only 1,200 miles on it. Some dealer in Texas specializes in these almost new police cars I believe. I think he buys them new from various agencies who order too many cars, and then he drives them for about 1,000 miles to sell them as used vehicles (maybe to get around some restrictions on sale of these cars brand new to public).