This project sounds like your ex creating a car he’d like to drive. He should keep it for himself for weekend driving and your daughter shouldn’t be let near it. If she really needs a car and you and your ex are going to get her one, make sure it is no more than a decade old, not at all sporty, reliable, not too tiny, and boringly practical. Oh, and let your daughter help pick the car as long as it meets the criteria listed. Get a copy of the Consumer Reports Used Car Buying Guide as it has all kinds of useful info, most critically reliability ratings. They aren’t perfect, but are good for comparing similar cars. They also have basic safer info and lots and lots of lists of recommended cars in various classes.
If it were my daughter I’d be looking for a boring Asian compact or mid-sized car. Unfortunately, that is exactly what every other used car buyer is looking for, so you may have to compromise a bit. Hondas, Toyotas, and Subarus go for a premium over other similar cars, so aren’t usually great deals. Mazda’s are very reliable and usually go for a bit less, so can be quite attractive. Either a Mazda6 or Mazda3 would be very suitable. Their predecessors were the 626 and Protege.
The Ford Fusion was made in Mexico, but is loosely based on the Mazda6 and has its virtues. It is kind of boring, but very reliable (with the four cylinder engine), very common, and reasonably priced. I don’t know how much you’re prepared to spend, but if it isn’t much you may not be able to swing a Fusion a they don’t go back that many years. The Mercury Milan is essentially the same car except for minor trim differences. Domestic cars are typically less reliable, but if they’ve been maintained really well they can be acceptable buys. Consumer Reports will give you a sense of which models are complete dogs and what the weak points are to watch out for.
When you’re looking at older or high mileage cars condition matters above all else. That’s why it is a very good idea to have a mechanic look over a car before you buy it. If you can find a well maintained car with complete maintenance records, super, but for older cars that can be hard. At the very least you need to know what major bits have been repaired/replaced. For cars that have timing belts you need to be sure it was replaced if was supposed to be, and budget for its replacement if it is overdue or upcoming.
Good luck with this. By no means let your ex talk you into letting your daughter have the Chevelle. I’m sure it’s what he wishes he had owned at sixteen, but that was then, not now. Your daughter may not even want it that much. If she does, work the safety angle. Look up how much higher traffic fatality rates were in the early seventies. It will alarm you, if not your daughter.