Ok here you go, here is the location of the serial number on the frame of a 4AD, see the little chalk mark ? that is where it is, trust me its there and its HARD to find under all the rust, dirt and "stuff"

On this one you see the measuring tape, it sitting on the frame support for the body. The measuring tape is touching (not visible in this picture) the metal bracket welded to the frame for holding the body down, this gives you a location for the serial numbers on your car.