Mike, current NH law says a car needs to be titled/registered as the year it was manufactured. There have been a number of Cobras registered here as 1965, but that was because of ignorance or leniency on the part of town clerks and state troopers involved.
Based on my experience last year, if you have a current title, it's a pretty sure thing that it will be registered according to that, no matter what year the title says. So if your title says 65, you are golden. I jumped through hoops trying to get my Hi-Tech registered as a 65, but was unable to do so.
Here's the discussion of that experience...you can see the inconsistencies.
Registration in NH?
Bill