RE: High Elevation Archery Elk Hunting
Personally I think the key component is that you're going on a guided hunt. Guides are used to flatlanders and people not in shape and can adjust the hunt profile to some degree. At the same time I agree wholeheartedly that you should be in the best shape you can possibly be. I've always done DIY elk hunts where you spend a lot of time hiking your butt off for days just finding where the elk are.. Guides tend to have that nailed down better.
You can nail down your pins quickly on site. I would practice doing some "out of breath" shooting because you will be short of breath often.