Ford Repair: 65 Mustang engine Identification, 302 v8, mustang engine

Question
I am restoring a 1965 mustang coupe that my grandfather kept in his garage for 25 years.  He believes the 289 V6 was switched out for a 302 V8 but is not 100% sure about the year.  What are some ways to identify the year of the engine?  The only casting numbers I see are 3J23.

Answer
Steve-

  Well...there's very little difference between the 289 and 302 V8s that came with the early Mustangs.  If it's original it's a 289 because the 302 didn't come around until '67.  To make sure, you'll need to check the part number which should be on the passenger side rear of the engine block just above the starter.  Hope this helps.

Steve