Fords of this era don't have a serial number or VIN stamped anywhere on the motor. What they do have is a casting date (should be cast into the bottom of the engine below the oil filter adapter) and an assembly date (stamped into a pad towards the front of the engine, I believe on the driver's side). Take a look at this thread on another forum for photos and more information on how to decode:
Block #'s revisited - Vintage Thunderbird Club International
~Steve