The 1963 Buick Riviera Silver Arrow I Buick concept car was a production Riviera coupe specially customized by GM styling head William L. Mitchell. The car served as a personal vehicle for Mitchell when not being shown, much the way early Buick concept cars had for his predecessor Harley Earl. The roof was lowered, and the front fenders lengthened several inches, housing the concealed headlights.
There were two more versions of the Silver Arrow I. The Silver Arrow II and Silver Arrow III incorporated unspecified but relatively minor changes to the production Riviera.
Source: Bill Bowman - wiki.gmnext.com
Images: General Motors Corp.