Interesting if alarming!

I would imagine The symptoms would end up being similar to tight valve clearances on an old mechanically adjusted engine.

Compressions might be good, but HC would be very high and inlet manifold vacuum poor.

The engine actually starts and drives reasonably well.

But how would one check this possibility without stripping it down??

In the old days one might check and adjust valve clearances. However with Hydraulic ones I can certainly see how they might go "Tight"(By ending up at the end of their adjustment range) but cant really see how one might easily check this other than by inference??

(Manifold pressure etc)

In my OP I said that the relatively high HC might bee a clue, thinking about it the low O2 and NOX might also be one (The Cat is actually doing its best) but the incorrect manufold vac might be producing an overfueling situation that the cat cant cope with.

Ho Humm,

Will report back later