Dig the root ball. Leave as much as you can as far as roots, but prepare them on-site as you would be putting them into the pot/box. If you will be potting the tree within a couple hours, no reason to take 100lbs of dirt, only to scrape it off in your driveway. But, leave absolutely as much as possible undisturbed. Also, wrap the roots in burlap to help keep them moist. If it is hot and dry, wet the burlap. If it is too heavy to carry, you can drag, roll, pull, push, whatever. Put it on a tarp and drag it. Get a backpack and strap it on. Be creative.
Good luck!