my dads did a bit, they put this !Removed! protection gunk all over the engine and that tends to smell a bit, but as you say depends on what it pongs of
best bet matey, it's not that rare in the UK now.
You'll need to sort the details with DVLA, which may be PITA, but worth doing so no issues down the line
neither of my engines have been and they have both been crackers. As you say opinions seem to vary on whats right and wrong, my advice is go with what your builder says.