Classical music has long been a source of inspiration for pop. Just ask Barry Manilow ("Could It Be Magic"), Eric Carmen ("All By Myself," "Never Gonna Fall in Love Again"), Billy Joel ("This Night"), or Walter Murphy ("A Fifth of Beethoven"). Ace Records has recently collected 24 of these classical "crossovers" on the aptly-titled Classical Gassers: Pop Gems Inspired by the Great Composers. These tracks date between 1960 and 1971 and feature such hitmaking artists as Lesley Gore, Jay and the