I'm certainly no accomplished high altitude driver.
I used to live at 9500 ft and from time to time go to some places at higher elevations, but never changed the setup that I had for my daily driver routine, which basically consisted on running the Hitachi VC42 carb with a 125 jet, instead of the 135 for sea level, and also advancing the timing to 13° BTDC, instead of 10°.
Since you loose some compression at higher elevations, you can advance the timing a few degrees without risking having piston knocking, and gaining a little bit of power in the process. In fact, the owner's manual calls the screw that secures the distributor base, "octane selector".