It's important to follow the rules for your state/ province/ country. Here in Ontario, assuming it is built on a Fiero spaceframe, you register with the Fiero VIN but identify it by the body kit name and manufacturer. Instead of Pontiac Fiero, mine gets labeled as INSP, VENT (since it is an Inspire Composites, Venta-R body). If no VIN were available, then it would be registered as "homebuilt" and they assign a VIN. (Used if you build using a tube frame chassis).
Insurance is determined from a professional appraisal... and you need to insure with a company that handles kit cars, etc. Contact your local DMV (or whoever regulates it where you are) and check the procedures.