Eric's situation is extremely common; as it was standard practice back then to date the car from when it was sold rather than when it was made. My "59" TR3A was made in 58, and my "57" TR3 was made in 56. Most obvious example was the Sports 6, which was sold as a 1965 model but made in 1963!
But my experience has been that, for cars that old, the DMV isn't too picky and will use pretty much whatever it says on your paperwork. From their point of view, it doesn't make any practical difference. My suggestion would be to go to them first ... if they want more proof, they will tell you what is acceptable. To some extent it depends on which clerk you get anyway, and they are always happier if they can send you away a few times first.
If you really want proof, fabricate a "STC" plate and pop-rivet it somewhere. These were apparently added by some dealers starting in the early 60's, to "prove" the car's model year.