It's a gorgeous route, but I'm not really sure what sort of advice you're asking for. Do you know about changing carb jets for altitude? If you're going to do this, make sure you switch them back before descending or you'll do engine damage. I rode that pass (and others) with stock jetting without serious issues, although I was on a bigger bike (650) with more reserve power. People also talk about opening the airbox for better air flow at altitude; I didn't do this either (too lazy, too simpleminded), but it makes sense. It gets dusty, so make sure you've still got good filtration if you start messing with your airbox.

The only other bike issue is fuel: as best I remember it's almost 300 miles/500 km between fuel stops. The Argentine border post had gas for sale, presumably pilfered from official supplies. Don't hesitate to take advantage if there's any chance you might run short; it's a desolate place to get stuck.

Allow enough time, and try not to be up on the altiplano after dark. At altitude it'll probably be waaaaaayyyyy below zero (C) at night, and there are vicuñas wandering around and other road hazards. Basically, though, there's nothing wrong with the road surface--it's easier than Ruta 40 ripio, with just a few sections of accumulated loose sand or gravel.

Hope that's helpful.

Mark