I'm building up my old Litespeed Classic frame with semi-horizontal dropouts as a singlespeed. I'll probably be running a 42 up front. My wheelset is an old set of Campy freehub bodied Spinergy Rev-X's. I'm thinking of using 2 or 3 cogs on the freehub body for quick gear ratio changes. Hopefully the dropouts can handle maybe up to a 6 tooth difference.....we'll see....
I'm going with with moustache or drops, and both front and rear brakes. This bike should weigh almost next to nothing....