Your engine is from the Mk3 model - you put your question in the wrong forum section.
The figure shows where to look for the engine number.
Since your engine is from 1986, it probably has a CAV Lucas injection system and has the symbol 4AB. The next eight-digit engine serial number should be the same as the last eight digits of the VIN number if the engine is original and not replaced. But that's not your case.
Often the area is dirty and the number is illegible or even invisible. Then you need to clean them with a coarse cloth containing a petrol solvent.
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