There are two areas of law often confused, Federal law which supercedes all State law and State registration requirements. First the Federal law. It has changed since Amerisport was in business. Twenty five year old, not including current year cars may be imported without any issue. All motor vehicles that are newer, must comply with DOT and EPA reqirements for year of manufacture at a minimum. So, a GT5-S made in 1989, must meet 1989 DOT and EPA pollution requirements. You would need an engine built to those standards. Do you want to pay 60k to 80k in Europe for a Cleveland equipped car, to replace the engine? And with what, a smog legal Mustang 302? Next the car would have to achieve the DOT crash and other standards or apply for a waiver from the DOT. Not fun. Last, this process must be performed by a Federally licensed importer, certified Federally to do the conversion. Also, once imported and certified it is illegal to modify the engine for example. Most importers will not take a car like a Pantera because they have NO experience in meeting the Federal standards for this car. So, any car that circumvents these procedures is illegal and may be seized on the spot. You would have to make it comply within thirty days or the car has to be re exported or crushed. There are racing and show and display waivers with limited mileage, certified owners location with the inability to modify in any way the power plant and pre-certification of any future buyer of the car and so forth. If you have an accident and it is discovered you are driving an "illegal" car that does not comply with Federal law you might have a real serious liability problem. States are not required to investigate Federal compliance and may have additional smog requirements or not and may register anything, but this has nothing to do with Federal law. A title and registration by a State does not make the car legal Federally. I heard of a state trooper stopping a GT5 or GT5S in the southwest and he noticed no Federal placards, called the car in and it was seized. I can not say if the story is true or what resulted, but the description is in conformance with Federal law. Crazy huh? If you put non DOT approved brakes on and have an accident?? California through CARB has tougher EPA requirements than the Federal rules. In California for example, smog testing for twenty five year old cars has ceased. That is the smog test law. California HAS NOT dropped the requirements for original equipment on cars. So, if you have dropped a hot engine into your car, or modified it with parts that are non CARB approved you are in violation of California law. Will you get caught? Probably not, but if you do you will be required to return the car to OEM standards for year of manufacture. Now you know all the "whys" it is difficult and expensive and at the end of the day, not done much.