I can appreciate the fact that the guy did it and made it work, this is not an insignificant undertaking. But there are some basic facts at work here.
I think that pickup is woefully overloaded regardless what other "after-fixes" have been added to the suspension and the chassis and going around the corners probably produces some "spectacular frame roll".
Having 2-3,000 pounds of pin weight in the bed helps some, but I wouldn't drive that sucker loaded with the Smart bobtail except straight and level and only for a short distance. The center of the gravity on that pair is probably at the level of the drivers head, you take a corner with it at any speed and watch it lay on its side.
I know, I added a hoist 12 feet up on my rig.
It only weighs around 500 pounds and the truck felt like it was going go over after I mounted it. And that's on a 20,000 pound truck, I take corners gingerly when I'm driving it solo.
I can only imagine what 1,800 pounds feels like up there on 8,000 pound pickup. Yahooooooooooooooooooooooo!