Get under and look at it. I have the same thing on my bed. It has 14 guage diamond plate on it from prior owner.

But it is only bolted in like 4 places. The four original bolts that should have the big washers on them on top of the wood. There should be 8 but They only used 4 through my metal plate. Two in front and two in back.

So removing those lets me move the whole bed up with the boards and all still attached to the top steal plate.

Just get under there and look around. See how they did it.

Mine is also spot welded to the rear cross sill and to the outer 90 degree angle bracket bolts on the sides.

I plan on grinding it off and replacing all the strips and bedwood as it is totally rotted out.

I will probably remove the fenders first so the bed will be flat and not damage the fenders if I drop the bed. I want to take the bed off to clean the frame/chassis and springs and all.