Even though a bout of “sudden and brutal” bronchitis kept Barry Manilow from his preview performances on Broadway, producers have promised us he’d make a full recovery for his opening at the St. James Theatre tonight. Manilow appeared yesterday on Katie Couric’s daytime show and didn’t seem that croaky, singing hits including “Mandy.” Tonight’s after-party will be at — of course — the Copacabana in celebration of the Manilow hit. “Copacabana” songwriter Bruce Sussman and Manilow created another Broadway-bound show, “Harmony,” which opens in Atlanta this September. We’re told Copacabana security’s been beefed up for a swell of guests expected to include Clive Davis, who gave the singer his very first contract.