Maybe it’s just me but I don’t think burying a car helps preserve it very well. Also the Plymouth brand is now part of the past and no longer made.
That doesn’t make any difference; the car is 50 years old anyway. Any car nut will take it and restore it.
The car is in a vault. Not sure all the prep done for it, but it’s not just dirt. Even if it was, you’d be surprised how well things like this can hold up truly buried.