They will find a ton of rust and seat cover fibers.
And a pair of mummified teens in the back seat.
"The Plymouth was wrapped in plastic and buried in a concrete tomb and placed on a steel plate so the wheels are off the ground. "
It will be interesting to see what they uncover, that's for sure. A '57 in mint stock condition could be a nice find.
Actually, probably won't be too bad. I'm predicting easily restorable.
I've seen cars buried in the earth itself keep their structure pretty well. I'm talking cars buried in the '20s and released maybe 50 years later.