okay but i can almost guarantee you that it will. All 3 KADE 240s that i have taken for e-test failed with similar readings, everything is good except NOx is through the roof. the timing was advanced to hell on one of them, the other 2 were within spec. retarding the timing made all 3 of them pass with amazing numbers and the tech that did the test couldn’t believe how well they passed.
high NOx is created from burning too hot, retarding the timing makes it burn cooler.
from my experience these engines run a lot better than stock with the timing advanced slightly (as long as you run premium fuel).
the mechanic is playing you for a fool and doing whatever he can to make an easy buck off you, and it’s working.