I've removed quite a few of these, here's what I would do.
Get new bolts and nuts. Steve's (toy4x4runner) came of an AZ truck, they are probably in decent shape. I also have an extra set. New ones from Sam aren't that expensive either.
Once you have them in hand, jack the truck up, get the weight off the front wheels. Put STURDY stands under the truck, you will be wrenching hard on things, make sure it's stable.
You will need a good long 22mm box/combo wrench, and a 22mm socket on a breaker bar, with probably a cheater pipe. You'll also need some zipties, duct tape, and a small chunk of steel, maybe 3"x3" or so.
Put the 22mm combo wrench on the upper nut, wedged against the frame, held in place with zipties. Duct tape the chunk of steel on TOP of the upper end of the long bolt.
Now, put the socket and breaker bar on the bottom adjuster bolt head. Brace yourself well, but DO NOT lay directly under the bolt. Now crank on that thing until you almost have a stroke. What you are trying to do is snap the bolt. When it does snap, the socket and bottom piece will come flying downward and smack the ground, so you don't want to be under it. The combo wrench will go flying, so the zipties keep it in place. And the upper end will fly up hard and strike the floor of the cab. I have seen these things actually poke a hole in the floor in that big dimple, so the chunk of steel will keep that from happening.
Slather the newer bolts with anti-sieze, install, and adjust as you need.
BTW, the '86-89 series trucks have 2 nuts on the top, the main one and a locknut. For some reason the next generation only has one big nut on top, no jam nut.