The documentation is as much as I have ever seen, it is just missing the dealer invoice/window sticker. Im not sure about what would be needed for the car to go back to the US??
I have been researching the Customs website (kind of unsuccessfully) and it is easy to get mirred down and lost there! But it seems the key is IF you have sufficient documentation that proves the car was manufactured more than 25 years ago it is exempt from having to meet the DOT/NHSTA and EPA requirements. I don't know what exactly they consider "sufficient documentation"? Model year on a title? Or a title from at least 25 years ago? Build Sheet (does a 1967 Build Sheet actually show the build date in plain language?)? Dealer invoice? I don't know. I'll try and find out more about this and let you know.