Hello, and welcome to the site. I assume you are asking if you have a numbers matching 65 Mustang. There were no numbers matching 65 Mustangs except for the K codes. What you have is an "A" code which is nothing more than a 4 barrel carbed 289.
In order to have a numbers matching Mustang, you would need the VIN stamped onto the block of the engine, and onto the transmission and rear end. That didn't happen in 1965. So, tell your dad that you do not have a way to prove that is the original engine for that car. The C60e block number seems to indicate a 1966 engine, and the water pump C80e seems to be a 1968 pump. So, you see, it appears you don't have an original at all. Just enjoy what you have.