Where can I find a large amount of data on crashes that have happened to answer the question
Which old cars (specific models and years) are you most likely to survive a crash in?
Obviously you would have to normalize these judgements using data on how long each model/year has been on the road and how many of them there are.
And of course with all this kind of data considered, such a ranking will still be "contaminated" with a lot of irrelevant factors that cannot be tracked, like how they were being driven at the time of the crash, and so many others. But even so, without needing fancy statistical theory or rich data, we can at least say "a car at the bottom of the list is probably less safe on average, discounting all other factors, than a car on the top of the list".