Disneyland is prepping for an invasion of Zac Efron groupies. Disney Channel has set Aug. 14 as the premiere party for “High School Musical 2,” to be held at the AMC theater in the Downtown Disney complex that abuts the happiest place on earth. (No matter how many times I go to the park I still choke up a bit at the plaque with the quote from Walt: “Disneyland is dedicated to the ideals, the dreams and the hard facts that have created America.”) It’ll be followed by an invitation-only party by the pool at the complex’s Grand Californian hotel. All the hoopla for “HSM2” marks the first-ever telepic premiere for Disney Channel at Disneyland, which is still recovering from the buccaneers bacchanal it hosted in May for the “Pirates of the Caribbean: At World’s End” preem. (Don’t forget, details of Disney Channel’s plans for “HSM2” bow on Aug. 17 appeared here two long TCA-filled weeks ago, thanks to Variety’s hard-working Steven Zeitchik.) And of course, a new live “HSM2: School’s Out!” stage show “springs to life,” according to Disney’s PR missive, at the California Adventure park starting Aug. 18.