The details on how to do what you want to do varies from state to state. Don't let anyone tell you anything unless it relates directly to your state. I am a licensed rebuilder in Illinois. There are easier ways to do this, but if you want to use this roll-over, I would buy a flood truck like yours (fresh water only, of course) and swap all that sheet metal to yours. Maybe even find one the right color.

Wherever the VIN numbers are located will need to be the parts and pieces that are kept together on the end unit. Everything HAS to match the title. As long as all the proper parts that have the VIN from the title are retained, you should be good to go. But check with your state people on this.

And be sure to understand your state's process for turning a salvage title into a rebuilt title. Without a rebuilt title, the vehicle CANNOT be licensed.