from DOT web site
http://www.nhtsa.dot.gov/cars/rules/...ges/page2.html
10. Importing a disassembled vehicle.
A disassembled vehicle that is shipped without an engine and transmission is treated for importation purposes not as a motor vehicle, but instead as an assemblage of motor vehicle equipment items. Such an assemblage can lawfully be imported into the U.S., provided any equipment included in the assemblage that is subject to FMVSS, but was not originally manufactured to comply with that FMVSS or was not so certified by its original manufacturer, is removed from the assemblage prior to entry into the U.S. Equipment items that are subject to the FMVSS include tires, rims, brake hoses, brake fluid, seat belt assemblies, glazing materials, and lamps, reflective devices, and associated equipment.
If the assemblage is shipped with an engine and power train (even if those components are not installed), it would be regarded for importation purposes as a motor vehicle, and would have to be either manufactured to comply with all applicable FMVSS, and be so certified by its original manufacturer, in the form of a label permanently affixed to the vehicle, or be determined eligible for importation by NHTSA and be imported by an RI or by a person who has a contract with an RI to bring the vehicle into compliance with all applicable FMVSS after importation.