Preservationists of Austin’s ruggedly eclectic heritage, “SouthPop” serves as the preeminent museum of our city’s music culture. Chief among collections of exalted ephemera are works of poster artists, from Jim Franklin’s Vulcan-ic psychedelia and Armadillo Art Squad sketches to colorful prints by Kozik and Kuhn. Concert photography and musical artifacts are also safeguarded at the Planet K annex, outside of which a memorial wall honors departed local heroes. “Open by appointment or by chance,” SouthPop is operated by veteran culture guardians Leea Mechling and Henry Gonzalez. Ask about the three numbers that unlock the universe: 709.