How to ID a 340

This might be a dumb question, but here it goes...

How can I confirm if an installed motor is a 340? I think it is on the pass. side of the block under the head? Can it be seen easily from above? Any pics to guide me along?

I have never actually cared to look at any motors I have had in the past, so I really have no clue... I am looking at a car this weekend, so I just want to be sure I know what I am looking for...

Thanks in advance!
Robb