Help with checking numbers

On my own car! I am not a numbers kind of guy, but was told when I purchased this 72 Duster 340 that the engine and trans were supposed to be the originals. I would like to try and verify that for what its worth. I know where the VIN is, but not sure where on the engine and transmission to look and what to look for. In 72 would those numbers be the same as the vin or possibly only the last 4 digits?

Thanks,