they are actually self taping screws, look underneath and use a phillips, i wroked at ford in the body sho for three years did plenty of them..........

 

i'd say the paint beneath will probably look funky, but you will probably be able to buff out the bad stuff and make it look decent....

 

If they are specific to that model, they may use existing holes for the fender liner in the front. Most that I have seen have self tappers/rivets into the flat part of the inner fender lip. You'd have to make 100% sure that you rust proofed the hell out of the vacant holes so no rust occurs.

 

There is a retirement community on Lumsten almost across the street from my old apartments (next to the old Brewhouse). Scope out some Grand Marquis there, see how the things are attached. They won't care, they're old.