With reference to previous absurd but technically correct interpretations of US national park rules[1] I'd like to suggest a way to comply with the rule in question [2], which states:
High clearance four-wheel drive
is required on motor vehicles
travelling on [...]
Take a 2WD vehicle, then bolt an extra set of wheels onto the drive axle (the tires are apparently optional).
The vehicle would still need to be high-clearance.
Or, if you're feeling really adventurous, just glue a set of LEGO wheels to the center of the hub. Those wheels would demonstrably have a high clearance, and comply with the rule as written.
> A Jeep, sport utility vehicle (SUV), or truck type with at least 15-inch tire rims and at least eight inches of clearance from the lowest point of the frame, body, suspension, or differential to the ground. Four wheel drive vehicles have a driveshaft that can directly power each wheel at the same time and a transfer case that can shift between powering two wheel or four wheels in low or high gear. All wheel drive (AWD) vehicles do not meet this definition.
Just in case it's unclear, I'm not being serious here.
Still, it seems to me that the wording still allows for some rules lawyering.
When they say "directly power each wheel" they clearly mean the four wheels attached to the OEM axles.
But I think their wording is open to arguing that it's any four "wheels" of your choosing, and now that your drive axle has two wheels on each side...
The rest of the wording allows you to flip between arguing on the basis of your now-four wheel drive axle and the stock axle. After all, they're not saying "those two wheel or four wheels". Different sets of four wheels on your now six wheel car should satisfy all the criteria.
However, the mention of a transfer case is a showstopper. I shouldn't have mentioned 2WD.
But given the above contortions e.g. a BMW X5 with 216mm (8.7 inches) of clearance should qualify.
The manufacturer obstinately insists that it's not an AWD, but "xDrive". The gear ratio of the AT even is so low that you can idle at a standstill while in gear!
The vehicle would still need to be high-clearance.
Or, if you're feeling really adventurous, just glue a set of LEGO wheels to the center of the hub. Those wheels would demonstrably have a high clearance, and comply with the rule as written.
1. https://news.ycombinator.com/item?id=36453856
2. https://www.nps.gov/cany/learn/management/compendium.htm