The car has to be at least 25 years old in Illinois, and with an AV plate you can register to use a Y.O.M. (year of manufacture) plate on your car and just keep the AV plate in the car, I've been looking for a good Illinois plate from 1972 but haven't found any cool enough to buy for my car.
The actual restrictions for driving with an AV plate are not upheld at all. I've never been pulled over, but for people I know who have and use AV plates on daily drivers it doesn't seem that anybody has ever cared. If I do get pulled over I could claim I'm using my 1k miles if it's not locally, if it is locally where they see my car going to and from places all the time I can say that wherever I'm taking it, I'm taking it there to tinker on it. e.g. school, parts store, friend's house. If all those fail I hand over my get-out-of-jail-free card that's the card of a Captain in the state police who's family.
Anywhere I drive my car IS a demonstration.
I don't wear the 3rd piece to my safety-belt, it's the shoulder cross that snaps into the lap belt, when I took my license test last year the lady who rode with me didn't wear it either since the car didn't come with them, they were put in by the first owner.
On old cars I've seen situations where wearing a seatbelt in an accident has caused way more damage than not wearing one, but I still wear my lap belt. My grandpa's neighbor had a Chevy II and he drove his friend around in it as soon as he got it running, he didn't wear a belt but his friend did, a car pulled out in front of them and they hit it at about 40 (the speed limit there). The driver broke his jaw on the dash board and was bruised up, other than that nothing bad. The passenger had his belt on and ended up with a lot of his organs re-arranged and torn up from the belt holding his body back from sliding forward. =/