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.

neat-o...... now sell it on craigslist.

Are you sure they are riveted? Because I just took apart the front chainwheel assembly on a peugeot mixte, and it was bolted together. Not with normal chainring bolts, but with weird short solid bolts, with a 10mm head and with the head on the inside of the chainring.

One warning: If this applies to you, those bolts are SOFT, so make sure they are soaked in penetrine or WD40 before you try to take them out, because they will round off in a second, as I found out

Actually, they aren't riveted. They're welded together. There's no bolts of any kind.

Grind the teeth of the 52 down to make a bashguard?

I considered that actually... one at a time with the dremel. I figured it would come out looking pretty terrible. So I thought I'd just tell people it's a chain guard designed to look like a chain ring... it's the new in-style.