Okay so this may be odd....

I have a 1970 Cutlass 4 door sedan with what I believed to be a 350 ci olds motor and it was so for several years, the mechanics said nothing about it, the guys at oreilys thought it was a 350, and the vin says it's a 350 but, when i took it to have a spark plug socket bored and repaired, the mechanic who knows quite a bit about the older cars tells me it's a 400, which I'm skeptical of, until well, i noticed that he compared it to a chevy 350, and my block is considerably bigger, but i've changed the valve cover gaskets with ones intended for the olds 350 2bbl, and they fit perfectly. And I looked up the records and it says that they stopped using the 400ci in 1969. Can someone give me clarification here?

 

What is the casting number on the shelf just behind the water pump next to the oil fill tube?