Appalachia and Los Angeles make unlikely bedfellows, but the self-titled debut album from The Sidemen is a seamless marriage of those ancient and current American folk traditions. The bedrock of the acoustic duo’s spare, soulful ballads, shanties, and “folkabilly” rockers is the vocal blend of veteran singer/songwriters Nick Justice and Feter Martin Homer. The pair’s impeccable musicianship — most of it recorded live on guitar, mandolin and banjo — is complimented by guests Gabe Witcher of the Punch Brothers on fiddle, and Alan Deremo on upright bass. The result is a startlingly intimate 10-song tour-de-force that serves to both document and expand on the group’s incendiary live performances, of which there have been more than 100 over their nearly two-year partnership.