anyone know how to tell if 4 speed is overdrive

supposedly small block a body, it came extra with a 3 speed demon I got. but someone told me its a PAIN to change from 3 speed to 4.... it says a body someone wrote on with a sharpie but I only know what I've been told

That is actually a SIMPLE swap.....is somebody trying to screw you out of a good 4-speed trans by getting you to sell it cheap?