Merely by copping to the magic concept "rockabilly," Cash can kick up comeback talk. And comparison with his rockabilly rockabilly for Sun (where he was always the countriest) establishes that by the standards of an ordinary mortal he's a better singer now--more flexible physically, more expressive emotionally. But the technique is a cover for what's lost, probably forever--stolid depth as immovable presence. Same goes for the arrangements--defiantly understated for Nashville, they're customized rock-country up against the austerities of the Tennessee Two. In other words, an honorable country album with some pretty good songs on it. B-