Hi Guys
I came across this information on another forum based website of which I am a member of. It pertains to the stamping on the original Nissan/Datsun jack and how it translates to the date of manufacture.
I have the original jack for my model year 1969 Datsun 1000. On the base of it there are the following letters stamped:
O A R
(Sorry I dont have any pics).
Based on Japanese date nomenclature, this stamping translates to a manufacture date of 18th January, 1969. 
First letter = model year (O = 1969 in this case)
Second letter = month (A = January in this case)
Third letter = day of the month (R = 18 in this case)
So my jack was made on the 18th January, 1969. 
It would be interesting to hear from others out there that have the original jack for their car. With this kind of info it helps to narrow down exactly when the car rolled off the assembly line at Nissan. The jack and spare wheel/tyre would have been the last things put into the boot to finish off the car. I am unable to find any stampings on my original wheels, whereas for my other Japanese car the wheels are also date stamped.
Apologies for no pics; car is in storage.
Bee010

Ive attached an example photograph of the jack stamping which I am referring to (borrowed from the other forum based website).

My jack is like this in the ute:  and I think it's original because the jack handle snaps into the wall behind the seats -  but no secret code numbers on the jack...