"Victor, you can get a manual
"Victor, you can get a manual for that from this site - just have a look at the upper right part of this page.
The only recommended plug for that motor is NGK BPZ8HS-10 gapped at .040" (1.0mm).
You didn't state whether this motor has carbs or is fuel injected. In either case there is no recommendation for changes running at a higher altitude. The only note that I saw regarding that was the fact that they produced a different lower unit gear for high altitude operation (to compensate for the thinner air/reduced rpms).
Mercury/Mariner has pretty much done away with the "exact" model year. Every motor in a given series will be/look exactly the same. They did this mostly so that a dealer won't have "old motors" in stock, plus, the motors just don't change any/if at all from year to year until they implement a new design.
Your motor falls into the "current" line. So, if a dealer still had it in his shop, he could sell it as a 2007. So whether it was bought in 2004 or 2007 makes no difference to the parts/maintenance of the motor."