“Hello!” Alan Dunham sings exuberantly at the beginning of his 1980 LP Flying Alone. “It’s nice to meet you!” Not too many people got the chance to connect with the teenaged singer-songwriter back then, though. The homemade album was released in minuscule quantities — a very private press, indeed. But in 2021, the ever-reliable crate diggers at Numero Group are giving Dunham a proper introduction: Flying Alone hits various digital platforms this week.