I have a 1973 Cuda with a build date of 12/13. My guess is it's 12/13/72, because 12/13/73 would be 1974 models.

Anyway, the motor is stamped 72. Might just be a coincidence, but my guess was that it is the year.

Is it possible that it is the original motor?

 

Yes very possible. as your car was made end of 72