I have imported quite a number of vintage cars from Canada over the years
primarily older English models. Austin Healys, some Aston Martins, Jags, ACs, etc
These were all project cars that I flipped with a bill of sale
no one I know of had any real trouble pulling an American title which is pretty much a State process
some States are a real pain in the ass, others dead easy
MN is pretty tough
they either want a bond filed on the title or sometimes one can obtain Sheriff's titles, etc
also loopholes for abandoned vehicles similar to mechanics liens.
depends a lot on your local jurisdiction really
Grey Market importing is much harder than it used to be however it remains particularly doable if you are overseas in the Armed Forces, State department, etc.
For example most of Saddam's son's collections of super cars ended up imported Stateside, most were gifted out to politicians and military brass
talking late model Ferarris, Lambos, Buggattis, etc
rules are only for little people ya' know