Thanks everyone for the replies. It would appear that the numbers have had different meanings over the years - chassis number, engine number or employee number ... or even nickname.
I don't quite understand the logic of matching the bonnet to a number stamped on the side of the engine, rather than the one staring you in the face on the chassis plate! However I can confirm that, as Arwyn and Richard both suggested, 3178 are the last 4 digits of my
engine number. I'm embarrassed that I didn't notice before!
~iw
