You will have to have it inspected first and everything must pass before you can get it registered and I guess it is tough in some states even for kit cars. Best bet would be to go to your local DMV and ask them what procedures you will have to follow to get it registered.
You will need a MSO (manufacturer's certificate of origin) for the major components such as frame kit, receipts for all major new parts, and receipts with VIN for all major used parts. The State will issue a "VIN" and the title will be issued as "New-assembled from parts" It will also require an inspection by the state DMV. (I do this all the time with motorcycles) Sometimes it is easier to have a licensed custom builder certify it and assign a VIN. (for a fee of course) Another option in NY for a pre-74 would be to find a registration for a junked car the same year as your custom body. Transfer it to you, as long as the original registration has not been issued a certificate of destruction. Then register your custom as the one you have the new transferrable registration for. Keep the original body ID plate and attach it to your rod for your annual inspection. You have restored your junker by replacing everything. (step 1 in NY is verify the serial or VIN, after removing old inspection sticker) The state's objective is to maintain a paper trail. They can really make it difficult sometimes. My last project took me 4 months to get the paper trail correct.
Here in Wisconsin the State Patrol does the inspection. The best way to go about it here is to have them come by everytime you do major work on it. This is so they dont have to tear through the entire car to check everything is what thhey told me. I think the trooper just liked to see it all come together. The best part was making a friend for life. But check the DMV or the State Patrol. But be causious, at least here, there are all kinds of regulations to go by, from headlight possioning to bumper hight and so on. I would get a list of the regulations before you start. And thats the best two cents I can give you.
Later..........And good luck.