Between the two of them, these old sidekicks have turned out a small, library full of records, and there are precious few letdowns among them. These two albums are typically entertaining, mixing small surprises with the integrity of consistency. Cash, for instance, does an Elvis Costello tune, The Big Light, as well as the Merle Travis country standard Sixteen Tons and the single by Bobby Braddock and Charlie Williams, The Night Hank Williams Came to Town. Jennings shows up with Jesse Winchester's Defying Gravity (Executioner's Song), Shake Russell's Deep in the West and his hit single Rose in Paradise, by Stewart Harris and Jim McBride. A song of McBride's about a construction worker, Heavy Metal (Don't Mean Rock and Roll to Me), written with Guy Clark, is on Cash's album too, as is Jennings himself, singing backup. For two men who are not exactly ancient (Cash is 55, Jennings 49), they have seen a lot of water go under the bridge, and a few other liquids too. They've both changed labels in recent years, almost always a sign of one kind of turmoil or other. (This is Jennings' second LP for MCA, Cash's first for Mercury/Polygram.) The titles of the albums, though, suggest the kind of pride and independence reflected in Cash's and Jennings' music. To paraphrase a song on an old Jennings album, they may be used but they're hardly used up.