Are you referring to the hidden VIN numbers? There may or may not be any as the government just started requiring VIN stamps on all pieces of a car to combat auto theft rings about that time frame. Usually if they are there they are stamped on the top of the frame where it travels under the rear seat and can be seen with an inspection mirror if there isn't too much corrosion and road dirt caked on.
I recently had the body of my 70 convertible off, and after blasting the frame, found NO VIN numbers anywhere on the frame. But on the left rear side of frame where resonator sits,were some numbers and the letters "BUDD". When the a/c evaporator box was removed from the firewall,the VIN showed up twice.