My bushing bolts would not come out, even after soaking in rust blaster spray for a couple of days. The bolt would just spin and I found the best way to get them out was to cut a small hole inside the cab floor. I made a small foot print and then I made covers that I then screwed in place. You can see the cover plates in the cab picture. Making access plates made it possible to have access points for future needs and prevented the need to weld patch panels. I carefully measured the location of the bolt nut then cut a 3" x 1 3/4" for the rear cab bushing holes (the size is important to cut inside the floor supports which are 2" wide, so the cut is hidden from under the truck) for bolt access. The front holes are about 2" long (wide) instead of 3". I then fabricated the covers for the holes.
The nuts are in a nut plate and as you can see in the two pictures they just spin. The metal on the side of the nut plates is weak and gives way, allowing the nut to spin. To solve the problem, I cut two 1/16th to 1/8th pieces of steel and welded them in place on each side of the nut plate/nut. They have to be welded because the torque of the nut when you install the bolt will throw them out. The only way the bolts would come out is by heating the bolts threads with a torch, then they could be removed when you keep the nut from spinning in the nut plate housing with a couple of screw drivers. The appearance of moisture is all the oil I had used to try and loosen the bolts (without any luck - only heating with a torch worked). Afterwards, I cleaned, rust treatment, metal prepped, KBS rust seal, and the after drying I re-tapped the holes to ensure the new bolts would go in easy (with grease).