635 CSi engine number - location?

[griffter]

Hi, I viewed a 635 yesterday but couldn't see the engine number on the block (even with torch and dentists mirror!). Can anyone give me clear guidance as to where it is located please? A picture would be great. I had a good look under the inlet manifold where I was led to believe it was located (somewhere) but couldn't see anything stamped.
Any advice appreciated - thanks.