First of all, let me say one thing:
You should not fly in mountaineous terrain if you havenīt been trained to do so in the past by qualified instructors!
I spent a fair amount of my time flying in mountains and at high altitude, doing slinging, long line, Search and Rescue as well as Passenger transport, and have seen to many pilots flying there without proper training....which is deadly, there is no grey area on this.
Second, you will need to know the wind situation, and the power reserve for each approach-you need to approach in a way that allows you to always abort the approach and have a safe escape path, or to continue the approach should one engine fail.
In your example i would suggest to approach steeper-than-normal; a 4-5 ° approach would be a "normal" approach-i would tend to more than 10° (but this is difficult to say without knowing the exact details of the landing site)..
My highest landings were only around 16-17000 feet....probably other guys here with more insight at higher landing sites?
This could give you a little bit of background:
FAA