What could go wrong? Cross country trip

So my son (23) is a mechanic who currently works at Toyota and is quitting to go to school and become an aircraft mechanic (like his old man). He is going to take a few weeks off and between leaving Toyota and starting college. My father owns a home in North NJ ( Bayville). My son was going to fly there and stay a week or so and visit as a summer vacation. Then I made the joke, really to shock my wife, you know what would a great trip? Jump in the (1970) Dart and cruise across country! Well..... now he is trying to make this happen. I don't think I would have thought twice about doing this when I was young but now being a father, I'm just thinking of the thousand things that could and will probably go wrong. He will not be driving alone, he will be with his girlfriend of 3 years. The engine and transmission were just gone through and rebuilt 3 years ago, full suspension done at the same time. About the only thing that has not been replaced or rebuilt is the rear end. The rear is a donor out of our donor car (1973 Dart), non sure grip, which has been serviced but not rebuilt. That car had 75K miles on it when we got and pulled her apart.

They would go north and across from here to keep a bit cooler but they are looking at doing this in July. He starts school in August. So now the wife is pissed at me and I'm kind of trying to talk him out it but also think it would be a amazing trip.

Thoughts on downfalls, if he actually goes?