I've got a friend that just bought a motor and he isnt sure if it's a 289 or a 302....how do i tell?

 

just a couple thoughts are they are hard to tell from the outside
asssuming its a older model
if it has a 3 bolt harmonic balancer it more then like is a 289
as the 4 bolt ones started i think in 70 and that would be a 302 for sure, also above the starter it has casting numbers and if its something from the 60's its would be for instance c8ae or so, the c stands for 60's and the 8 would the year, d would be 80's something
hope this gives you a clue........................