I bought my '69 Z/28 out of Canada (it was sold there new), brought it across at Port Huron/Sarnia. All U.S. Customs needed was the Canadian Registration (same as a U.S. title) and the Bill of Sale with the price on it and buyer and seller signatures, and for $5.00 they issued an "Informal Entry Certificate" - that's the document you MUST have when you go to register the car at your U.S. DMV. No taxes, no duties, no nothing - took about ten minutes.
