Guy Clark is a slow worker. Dublin Blues is only his seventh album since his debut, "Old No. 1," appeared in ´75. The silver-haired Texan has praised the patient, meticulous process of hands-on craftmanship in songs like "The Carpenter," "Boats to Build," and "Jack of All Trades," and obviously applies the same approach to his own songwriting. The time is well spent, for this batch of songs resembles fine furniture; the words and music fit together so precisely that there´s nary a seam nor a wobble. Clark´s limitations are the same as ever. The cramped dimensions of his vocal tone and range make Johnny Cash sound like Luciano Pavarotti, and his easy-going, clip-clop midtempo rhythms are too unvarying for their own good. Admiring friends such as Nanci Griffith, Emmylou Harris, Kathy Mattea, and Sam Bush make the harmonies surrounding Clark especially rich on "Dublin Blues," and Ramblin´ Jack Elliott (the subject o