This is a picture of a 71 Challenger that 68HemiCharger was doing some work on. Notice the factory black out on the ends of the rear seats where the seat and rear panel come together.

The amount and even the number of places blackout was put in the interior varies per car. But if you're looking at a restored E-body with a bright colored paint, look in the rear seat and you'll notice if they put black out on it for not.