Need help IDing my 340 motor

The build date from the fender code is 903 which I think is 3 sep 70. Makes sense to me that a 71 model would be built in fall of 70. Don't think the motor is original based on not finding a vin match and the dealer remembering a wrist pin failed and trashed a cylinder. I bought the car about 10 years into its' life. Would be nice to know more about where the motor came from...definitely appears to be time/performance appropriate to a novice like me. (Roll in here experts and correct me if I'm off base) Can't seem to find a decoder on the web for the nums stamped behind pwr stg pump on block...if anyone can decode or has a site I'd like to hear from you. Thanks!