If the car was originally registered out of the U.S., and is less than 25 years old, you will likely have problems with multiple agencies. If you provide, or have provided, false info to get the car into the country the government shutdown could be a blessing for you. Or, you will be in a massive world of hurt.
If it has never been registered before, and arrived in the US as parts (kit), you should have a Manufacturer's Statement (or Certificate) of Origin. Take that, and all your receipts for parts, assembly, etc to your state licencing agency. You might want to call them first to confirm exactly what you need because each state is very different.
Good luck.