As much as we may all be curious about how this will all play out, I wouldn't be eager to post again (yet) if I was the original poster. They've got a lot at risk and may not want to share any more info until they've had a chance to sort things out with the seller. I'm hoping that some of the advice on this thread will prove to be helpful.
As I understand it, the husband sold his Corvette in order to make them an all Mopar household. I sure hope this doesn't turn out to be that some scumbag took advantage of them.
I can't 100% honestly say what I would do in their situation. I'm sure I'd be in panic mode right now. If doing things 'by the book' means contacting the authorities they may have the vehicle seized. Even if they did nothing wrong they could lose a lot.
If it does turn out to be a stolen vehicle and the original owner cannot be found, they still may not be allowed to keep the car. I don't know how the state will react.
This should have been a happy time for them. Instead they're probably stressed out. It looks like a great car. I'm still hoping that this all turns out to be nothing more than a VIN tag removed during restoration.
There are methods of obtaining another VIN tag. One would be to find someone with a junk '68 Roadrunner and the owner still has the valid title and Vin tag. This is where a person's integrity comes into play. I wouldn't go that route unless I'd made certain the car WAS NOT stolen. Otherwise you'd be participating in perpetuating a crime. - And you'd have helped to separate an honest person from their car. It's a test of their own honesty. They do need to figure out if the car was stolen first.