what are the current laws that permit a vehicle to slip through emissions and street legality regulations?

i know you can run straight pipes on any vehicle made before 1974 or whenever. you can also put superchargers on it and make it around 900hp for a pro street. but what about all those people who build hot rods with tons of power and get away with it. they are'nt even remotely similar to the original car. couldn't someone build a modern supercar, put an old engine in it and call it a 1969 corvette? i really need to know the laws on this kinda stuff and where to find it. i am seriously considering a project of the sort with fiberglass molding for the body and alluminum welded chassis.:sun: