Dunaruna is right but here is a site that was given to me by EricKems. If you were like me with a Canadian serial number from an old motor, you must have called local dealers and they couldn't find it to help you. Frustrating search until I found this forum.
This page is specifically for your motor. If you browse through the site you will see that it is a great cross-reference for USA and Can. Mercury serial numbers.
thku for the info on this 1978 80hp unfortunately its now a parts motor hole in the lower part of the block below the bottom carb.... was just wondering for advertising the right year ..............