A common theme among today's rockabilly groups is purism. Often, bands measure themselves by how authentic their look is, how old their equipment and pomade is or how many original parts went into restoring their '57 Chevys. It seeps into the music as well, and there are schools of guitarists who base their careers on knowing each and every lick Eddie Cochran ever played. Paul Galaxy and the Galactix, who open for Brian Setzer's '68 Comeback Special on Tuesday, July 31, at the Fox Theatre, are plenty authentic. The pompadours are sharp, and the fins on Galaxy's Oldsmobile '88 are even sharper. But they haven't forgotten what year it is, and the end result is a sound that's forged in early '50s rock and tempered with everything that has happened since. There's a sense of showmanship and -- dare we say -- glam when the trio hits the stage: It's obvious that the distance between this group and the '80s hair bands is less than the length of the hair itself. Galaxy's blazing guitar work and frenetic stage presence are surprisingly powerful. Brian Setzer might find this a hard act to follow.