In addition to what other commenters mentioned, in some states there is a legal gray area for registering a vehicle as just modifications on top of a donor vehi

In addition to what other commenters mentioned, in some states there is a legal gray area for registering a vehicle as just modifications on top of a donor vehicle that's already street legal. Commonly you start with a donor as a base anyway and no one is going to independently verify that your mods align with DOT standards.