1977 Pontiac Ventura. It's the same model as James Sunderland's car from Silent Hill 2.
Chrysler LeBaron
Silent Hill 3 (2003)
That looks more like a 1979 Chrysler LeBaron than a Plymouth. It even has the Chrysler hood ornament.
Pontiac Ventura
Silent Hill 2 (2001)
That's a bad view of the car, but they use the same model several times for "parked" cars in the town of Silent Hill and you can clearly see the front on those. It's not a Nova. It's a 1977 Pontiac Ventura. (Note: I know the year for certain since the 1976's looked completely different in the front and Pontiac never made a 1978 Ventura.)
Dodge Diplomat
Silent Hill (1999)
1979-1981 Dodge St Regis. They were really popular police cars at a time. The designers probably found a picture of one and used it as the model.