Applications are available on-line.
Self-Assembled Vehicle Application
The only other thing some need to consider is the emissions issue. I got a "Lifetime Exemption" after jsut 5 minutes at my local EPA office (Middleburgh Heights, OH)
I gave them a photocopy of my private party sale that said my engine was a 1977. Coincidently 25 years is the cut-off for emissions requirements as well. This, despite the fact my car is titled as a 2002.