seem to be the only mods except maybe the air cleaner and and decals. Well, and wheels/hubcaps...
Hmmm, maybe not as straightforward as I first thought, but the body, chassis, engine, etc. would be close if not exact and the updated to '98+ Crown Vic to police, fire, taxi, and civilian or combinations version kits would probably sell well, which I hope would encourage some caster to do the Mercury.
1998-2000 Ford Crown Vic 4door sedan police
2001 Ford Crown Vic 4door sedan civilian
1999 Mercury Grand Marquis