That body number will be recorded on a Heritage certificate.

Thanks to everyone for your input. I have the number plate on the slam plate.

I have heard of VINs being stamped inside on the front foot wells and on the triangular reinforcing bracket on the bulkhead in the engine bay. I don't know what years/models or whether it is done consistently. 

Unfortunately the answer is ..no.  A 66S should have a "body number" stamped on a small plate spot welded to the bonnet slam panel. The  
BMIHT can tell you what vehicle that number was originally attached to.

And I would disagree with "66..S".  After 50 years its not surprising that lots of parts now post date the actually build date of the car.  Things break and get replaced.  

Anyway, none of the quoted parts are S specific and could come from any Mini of a similar vintage.

Its called provenance...  Unless you know for certain (having bought the original vehicle yourself - or perhaps your Dad did so you personally know the story)  you have to take what you're told, measure it against what seems believable, backed up by the consistent physical evidence/ documentation you have in front of you.... 

Cheers, Ian

Mini_Identification__Identification_by_Chassis_Number-VIN__Standard_Cars

Other than the chassis number aka VIN you will find some parts with a production date stamped (or printed/etched) on them - wiper motor, boot lock, glass, etc.  Hard to have a 66 when parts were made after the production date of the car

lots of articles in the articles section on identification.

Other than the serial number plate on a 66 S, was the number stamped anywhere else on the body?