K.C. and the Sunshine Band normally get pigeonholed as a nostalgic '70s footnote, somewhere between WIN buttons and Shaun Cassidy lunch boxes. But they were and remain more vital than that. K.C. and the Sunshine Band: In Concert is a 55-minute concert tape which affirms that Harry Wayne Casey (alias K.C.) ran one of the great dance bands of the predisco era, creating a signature refiguring of James Brown funk. Trousered in sparkling ''elephant bells,'' the group pumps out sweat-inducing renditions of hits like ''That's the Way (I Like It)'' and ''Shotgun Shuffle.'' Along with the propulsive bass lines (provided by K.C.'s cowriter, Richard Finch), the music was known for its Caribbean influences, evident here in the band's buoyant take on the smash they wrote for George McCrae, ''Rock Your Baby.'' Throughout the performance, this 12-piece band cooks up a sound most modern beat masters need machines to create.