That car was the Buick Blackhawk, announced late 2000, first displayed early in 2001, and linked to Buick's 100th anniversary in 2003.
The Blackhawk used the grille from a 1939 Buick and some parts from later models, though the design other than the grille was essentially new. I found no single source providing a nearly complete version of the Blackhawk's background, though various aspects are discussed here, here, here, and here.
The Blackhawk's concept theme is that of a "street rod" of the late 1940s, but with 2000-vintage details such as the wheels. Most of the photos below are either factory shots or are from auction houses publicizing its availability -- I'm not sure of most of the sources. The street view of a '39 Buick is one I took.