Chris,
The issue you refer to varies wildly from state to state and there is little, if any, consistency to the way it works. For instance, here in North Carolina, homebuilt/kit/custom cars are excused from emissions testing since the state figured none of them would have OBD-II computers and there are so few of them. This is a good thing, BUT the car will register as the year it is registered in. A bad thing if you try to sell it in a state with less rational laws. BUT when you go to insure it, none of the "standard" insurance companies will touch it and none of the specialty car insurance companies can insure it since they can only insure cars older than ~1976 because of the stupid insurance commission that NC operates under.
Tennessee registers cars as the year they replicate; which makes very good sense from a law enforcement perspective. California actually isn't bad as they allow the 1st 500 appliants to register kit/component/homebuilt cars with an exemption very similar to NC. Go figure that CA would do that, right?
If you do a search on this subject, you'll find input from guys from all over the US with very different stories from state to state. The guys in Australia have it pretty tough too as they have to meet all current standards to best of my knowledge.
Regards,
Lynn