I used to guide for a friend of mine who owned JW Outfitters near Gunnison, Colorado in the late 80's, base camp was about 9k. Boots, proper clothing, the rifle you will use and lots of time breaking in everything while training. This means you don't have time to wait for a custom build, I would peruse the classifieds here for a rifle, I'll bet what you want is already there, broken in and proven. If you want something new I would consider a Browning X-Bolt Hell's Canyon, the new versions have a faster twist, 24-26 inch barrels and muzzle breaks, Cerakote and lightweight, for an off the shelf rifle they're good. Kenetrek, Scarpa, Asolo, Vasque and many more are excellent mountain boots which I believe are an absolute necessity, properly fitted and broken in. I use Kuiu clothing personally but Sitka, Under Armor and lots of others have joined the technical clothing world for mountain hunting. Cabela's has some offerings as well but for my money Kuiu is the best. Unless the guide is doing all of the hauling in and out, you need a backpack that is designed to work in the environment, strong, light and can carry the animal with all of your gear. If your driving into a camp the pack doesn't mean as much unless you're hiking 5 miles in to start hunting. Perhaps all of this is moot as you may be an experienced mountain hunter and were simply musing about a new rifle which is not a bad thing.