Frank Zappa would have turned 70 this December — and the music world misses him still. Not just the rock music world, but also the classical music world, to which he originally aspired and which was just beginning to recognize his abilities at the time of his death from prostate cancer in 1993 at age 52.Frankfurt’s Ensemble Modern, the first group that was able to perform Zappa’s often-difficult compositions to his satisfaction, is taking Zappa’s music to the 64th Ojai Music Festival on June 11 as part of the group’s official West Coast debut. We say “official” because Ensemble Modern has been in Los Angeles before — but only under closed-door conditions. In 1991, Zappa agreed to work with the Ensemble after hearing one of their discs with music by Kurt Weill and Helmut Lachenmann. They traveled to Zappa’s studio at their own expense and rehearsed with him for two weeks, eventually coming up with a program of 19 short compositions and arrangements that formed “The Yellow Shark,” the last album released during Zappa’s lifetime. Not too long ago, it was difficult for many musicians and promoters to take Zappa seriously as a composer of concert music. His reputation — usually embellished — as an outrageous rockstar opened some doors for the occasional orchestra that wanted to grab new young audiences. But the rockstar image could only go so far with the gatekeepers in the classical ivory towers. Eccentric Zappaspeak titles like “G-Spot Tornado,” “Dog Breath Variations” or “Get Whitey” didn’t help his cause either. Nor did the Byzantine ways of orchestral and union politics. Yet now, as has happened so often with composers whose value was not fully recognized until after their deaths — Bach, Schubert, Mahler, Bartok, even Leonard Bernstein, as famous as he was — Zappa’s so-called classical compositions are becoming accepted into the repertoire. The Los Angeles Philharmonic — with which Zappa had a falling out following a notorious 1970 “200 Motels” concert at UCLA’s Pauley Pavilion — finally dipped a toe back into Zappa’s universe by performing “Dupree’s Paradise” in 2008 and took the plunge during its “West Coast, Left Coast” festival last fall with a program of excerpts from “The Yellow Shark.” As for Ensemble Modern, the musicians flew out to a Warner Bros. soundstage in Burbank five months before Zappa’s death to record music by Zappa’s idol Edgard Varese under Zappa’s supervision. Since he was too ill to lead the group himself, Zappa left the conducting to composer/conductor Peter Eotvos, while delivering directions from a sofa in the studio. It was Zappa’s last project — and though completed, it remains unreleased. At Ojai’s Libbey Bowl, the group, led by Brad Lubman, will perform selections from “The Yellow Shark” and a posthumous 2004 anthology of Zappa that the Ensemble put together, “Greggery Peccary and Other Persuasions.” As in the 2008 L.A. Phil concert, Zappa will be sharing the program with Varese, who will be represented by “Octandre” for chamber group and “Density 21.5″ for solo flute. In addition, on the afternoon of the concert at the Matilija Auditorium, there will be a symposium, “The World of Frank Zappa,” featuring members of Ensemble Modern and former Zappa sideman Ian Underwood. Gail Zappa, the composer’s widow who runs the Zappa Family Trust, has also agreed to take part in the symposium. In other Zappa family news, Dweezil Zappa — Frank’s eldest son and a whale of a guitarist himself — is issuing the second volume of his meticulous re-creations of his dad’s music, “Return of the Son Of …” on June 22 on the Razor & Tie label. This time, Dweezil expands his canvas to 14 Frank Zappa compositions on a two-CD set, recorded live on tour mostly in Chicago by the “Zappa Plays Zappa” band. Zappa devotees will recognize the title as a play-on-words on Frank’s instrumental-only “Return of the Son of Shut Up ‘n Play Yer Guitar.” The album is being promoted by a world tour, which played in Mexico City on Thursday and will work its way through the U.S. before hopping over to Europe and Israel, and the Fuji Rock Festival in Tokyo, Japan. And there is yet another posthumous Frank Zappa release from his apparently inexhaustible archives, “Joe’s Menage a Trois,” due on Zappa Records June 11.