I for one sincerely doubt that Superformance is declaring the chassis as "Motorcycle parts" to US Customs as it is not needed to import them. The cars are legit "rolling chassis component vehicles" and are legal to import and sell as such. Read closely in the NHTSA letter about the powertrain installation and what it entails legally.
Go to the
www.nhtsa.gov site and read the laws regaring component cars, they must only meet NHTSA standards for components, i.e. brake hoses must meet current standrds, glass must be certified, etc. NO requirements for crash standards, impact, etc.
There has been some comments here and elsewhere that that the Feds are trying to ban rollers, I have been unable to unearth any such info to date. If anyone has info to the contrary please post or link it here for our edification.
Rick