Well, that's a few good questions.First off, if you don't modify the chassis (stretch it), your car is essentially a Fiero with a body kit. Therefore, it should be just as safe (in the eyes of the insurance company) as an original vehicle. However, you'll be looking at them valuing the vehicle at Fiero prices, not 355 prices. You might want to look into 'stated value' insurance.
If your car is already registered - the chassis has a VIN number - you should continue to use that. It is illegal to remove a VIN number from a vehicle. If you are using a rebuilt wreck, and making into something that it's not, then there are ways of registering it so that it is a Specially Constructed vehicle. Of course, doing that makes your insurance go up.
The amount of your insurance is completely dependant on you, your driving record, and the insurance company you choose. If you go with a 'normal' insurance company, you'll probably encounter a few hassles when it comes to the body. They'll want to see pictures, probably the car, and receipts. You can go through some of the specialty insurance companies, but they can limit your mileage and where you can use the car.
If you do not change the VIN number of the vehicle, you don't have to go through any process (generally speaking) to register the car; it's still going to be a Fiero.
If you have any more questions, please feel free to ask!
Your pal,
Meat.
