As part of its William Finn festival, Porchlight Music Theatre Chicago performs Finn’s seldom revived 1978 pop opera about a sexually confused adolescent, Marvin, and the females in his life: the teacher he has a crush on, the girl he dates, and the woman he marries–and eventually leaves for a man, as we learn in Finn’s sequel, Falsettos. Like that piece (also reviewed in this section)–which is far superior thanks partly to playwright James Lapine’s influence–In Trousers is concerned with a transition to manhood in which physical and emotional maturity are badly out of sync. Matthew Gunnels’s brash, fast-paced, superficial staging obscures what subtlety the work possesses, and under Jon Steinhagen’s sloppy musical direction, the singers, especially the women, substitute loudness for clarity and energy for nuance. Through 4/17: schedule follows. 4/2-4/3: Sat 8 PM, Sun 2 and 7 PM. 4/7-4/9: Thu-Fri 8 PM, Sat 2 PM. Then Sun 4/17, 2 and 7 PM. Theatre Building Chicago, 1225 W. Belmont, 773-327-5252. $27-$30; $95 for a festival pass to all four shows.