I have a friend with a '91 Zuk (the only yr. fuel injected for import into the US, not carb. like an '86) and he had so little power even with 400:1 gear reduction with two transfer cases that he turbo charged the thing. It did work better at 10,000 ft. than before, but, my what a dog of an engine trying to roll those 35" tires. He finally just ripped off the turbo and chalked it up to experience.
In my view, in order for an '86/carb'd Zuke to make it up that high in any way, they would have to keep replacing the jets every 3000 ft. of elevation gain, with maybe 6 jet replacements enroute. Also, no muffler and a very large exhaust pipe; at least a very free breathing air cleaner with approaching zero restriction just to stay afloat. Not to mention the O2 masks the driver and passenger must wear after about 16K feet! Quite a feat in any case. Now this is assuming they are running a gas/carb engine. Many of these small Japanese 'jeep' type rigs were equiped with diesel engines from the factory. Maybe if they had one and turbo'd it?
No way I'll ever get that high.
You can see by the T.R. that our highest was 13, 200 or a few hundred feet more after Imogene Pass. The air was pretty thin, but the turbo diesels seemed unaffected by altitude, especially just plugging along using all that low end torque.
Every place we camped above 10,000 feet, we saw no one. It WAS far enough away.
regards, as always, jefe