Re: jetting for elevation
Running it with the existing jets will make it run rich and lose a bit more power than normally expected with altitude, but won't hurt anything. You may foul plugs easier though.
Look in you local library for the Intertech manual for old Chrysler engines. It lists every carb used and the jets for specific altitudes. You should be able to apply this info to your carbs since the jets are probably the same as in Chrysler 125 carbs.
Take along a prop of at least 2 inches pitch less, ie. if you are now using 17 pitch, try a 15 pitch prop. At that altitude, the engine simply won't get the air needed to develop its rated horsepower, and even with a jet change, will not be able to swing the prop you have on it now at the RPM you get now.
