I just converted a 10 speed mixte Peugeot to a single speed. I was amazed how easy it was. The dished rear wheel worked just fine as-is. I unscrewed the multi-speed freewheel and screwed on a 16T single speed freewheel. I removed the derailleurs and shifters and shortened the multi-speed chain. The bike already had horizontal dropouts and the chainline turned out to be perfect without a tweak.

The only thing a little odd is that up front I have a 52/42 chainring combo. Of course I used the 42 and the 52 just sits there unused. These chainrings are riveted together so no way to separate them. But I think it still looks pretty good.