I flat-towed my MJ with the Liberty once. I'll never do that again. It was one of the most white-knuckle moments of my life. your ZJ was never rated for towing that much weight without trailer brakes. be cautious. very cautious. Flat towing a rig (that's equal in size) is not like regular towing. the towed rig can push you around in ways you've never dreamed. you have to seriously slow down for turns or even gentle curves in the road. and the hitch rotates up and down, unlike a trailer. hard braking can then push the rear of your ZJ up or down depending on what's happening and on how straight it was while normal. Imagine a panic stop but instead of the front end diving down and planting, it goes up and gets light and squirrely as the towed rig tries to jump up into your hatch.
Emergencies are emergencies though
Does that only bolt to the bumper points? I would at least add a plate so that it stretches back to include the factory tow hook mounting mount. the factory bumper mounts were for collisions, not yanking on.