As muscle goes, Buick isn't the most popular of GM's divisions, but any adorned with red "GS" emblems were capable of serious performance, comfort, and class. Steve Magnante finds some GS high-performance equipment: the '66 Riviera GS, '69 Skylark GS 400, '70 GS 455 convertible and an ultra-rare '70 Stage 1 GSX.