I doubt that amphibious is a huge concern with that rig. you could remove the rear axles and relocate them an inch higher in the frame. this would make it turn more like a 6x6 on hard ground, but you would still have all 8 in the soft stuff. With some creativity you could make it amphibious even with that mod. Over inflating the 4 centers, or putting taller tires in the middle would have a similar effect. even try removing all 8 tires and see which ones are tallest at a given pressure. If by dumb luck you have the 4 tallest tires on the 4 outside corners, this will make it hard to turn
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