There are no regs on the building of a body except as to lighting, width, etc. None on the design or fabrication that I'm aware of after 43 years in the truck body/equipment industry. There are regs on the installation. OSHA has regs regarding safety concerns on dumps, i.e., the cab shield. It must cover the driver so it is different on each model of truck cab.
As to the rebuilding of one you are home free. Contact me if I can be of help to you.
