* For the large size and rear-wheel drive: The Dodge Charger (especially older models) or Chevrolet Impala (also older models) offer a similar large body size and rear-wheel drive configuration, though their handling and feel will be different. Modern full-size sedans are mostly front-wheel drive.
* For the simple, durable construction and body-on-frame: This is the hardest aspect to replicate. Modern cars are generally unibody construction. You might find some similarities in older, full-size American cars, but even then, the level of robustness and simplicity is rarely matched.
* For the police-car association and general appearance: The Crown Vic's boxy styling is difficult to find in modern cars. The closest might be older models of the Dodge Charger or Chevrolet Caprice, though newer iterations are much more styled.
In short, there's no single perfect replacement. The best alternative depends on what features of the Crown Vic you prioritize. If you specify what you liked most about it, I might be able to give a more precise recommendation.
