@Dog – You’re in CA, is that correct? I used to have a classic car and I remember at the time that prior to certain years, classic cars are grandfathered out of some of the requirements for modern cars, such as smog check. I seem to remember the same thing about seat belts, but I’m not positive about that. I took a look at the CA laws regarding seat belts and the information is somewhat confusing because they don’t have a section addressing classic cars directly. It does say that no car made after 1962 can be legally sold without the car having at least two front seat belts. Then, there’s the following, which kind of sounds to me like they don’t require seat belts if they weren’t required by law at the time it was first sold:
The safety belts shall conform to motor vehicle safety standards established by the United States Department of Transportation. This subdivision does not, however, require installation or maintenance of safety belts where not required by the laws of the United States applicable to the vehicle at the time of its initial sale.
Also, if you don’t plan to take the car on the highway, it sounds like you have even more leeway. I would call the DMV to check to be sure, as much fun as that is in CA. ;)