The Big O is back with a big box set.The MGM Years 1965-1973, recently arrived from Roy’s Boys, LLC and Universal Music Enterprises, chronicles over the course of 13 CDs (or 14 LPs) the least well-known period of the late vocal titan’s career. Orbison joined MGM Records riding the crest of the “Oh, Pretty Woman” wave; the composition which he wrote with Bill Dees was a U.S. and U.K. chart-topper at the height…