For legal height check with your DOT. Accepted height - above the scrub line. As I don't know the length of the body in front of the front wheels I can't even give you a ball park figure. Just remember that you have to go down and over the gutters of the road to get into parking lots, etc. If you can figure out what that slope is and use some trigonometry (always wondered when you would use it didn't you) you will be able to figure out how low you can go. Or you could just mount casters under the bumper.
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