I think you'll be OK going up in altitude although you might notice a little loss in power. Of course, the steepness of mountain roads might be the primary culprit.
When we lived at 7200 ft. in Laramie, WY, our car tuned for that would start to knock at Baker, OR on our way to sea level. I'd just use a mixture of regular and ethyl until be got back to Baker.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
