COUNTRY Ned Sublette and the Southwesterners: ''Western Classics.'' (Lovely Music VR 1401.) The high point is Sublette's solo rendition of the classic ballad ''The Buffalo Skinners,'' a ferocious and passionate performance in the great Eric Von Schmidt tradition. On the other cuts, he's accompanied by six old-time country musicians plucking, strumming, and fiddling their way through ditties with titles like ''Little Old Sod Shanty'' and ''The Forty Years Ago Waltz.'' A recognized ''new musician'' with credentials in some of today's most radical and exploratory work, Sublette clearly enjoys looking to the past as well as the future. The living spirit of American folk music abides in this eccentric but thoroughly engaging disc.