If the engine number is cast/stamped on the cylinder head and you fit another head only ie not a complete power transplant how does that affect the reg in the blue book.

Head bought with copies of original vehicle registration by the way.

Same make of engine not a change of type.

Engine numbers tend to be on the engine block rather than the head. Changing a cylinder head will not require anything to change in the book. There might be an engine type / model number stamped on the head but it has no significance to the numbers in the registration book

It's the only number I can see anywhere so far. Still cleaning searching.!!!

You don't say the 'Make' if not here try a google search with the make and engine size,

You don't say the 'Make' if not here try a google search with the make and engine size,

Did actually google and it gave me a location. Checked the location and no number.

Reworded the question and eventually found a post that indicated at one point in production it changed to the other side.

So tomorrow will be more cleaner, wire brush and sore back day. ?

l guess you will be Ok but why not pop along to a 7 year car test place or your nearest DLT and check it out, no worries.