Two seemingly disparate '70s acts will become one on Friday night, when the local cover band Groovethang transforms into both Steely Dan (as the Showbiz Kids) and Earth, Wind and Fire (in the guise of Shining Star). On the surface, not much unites these two musical behemoths. One is a wry, literate group of studio rats specializing in songs about deadbeats, losers and aging hipsters. The other is a platinum-clad funk and soul powerhouse that crafted effervescent slow jams and bombastic barnburners. But a closer examination reveals that the pairing is inspired: Both bands played polished, intricately arranged soul music that could kick your ass at the drop of a drumstick with ace soloists and hypnotic grooves. And where else can you sing along to "Rikki Don't Lose That Number" and "Reasons" in the same night?