Complex sentence: The storefront beside CBGB became the "CBGB Record Canteen"--a record shop and café--converted in the late 1980s into an art gallery and second performance space, "CB's 313 Gallery".
Split into simpler sentences: The storefront beside CBGB became the "CBGB Record Canteen", a record shop and café. In the late 1980s, "CBGB Record Canteen" was converted into an art gallery and second performance space, "CB's 313 Gallery".