OK- THANKS EDThis site sez it's an '82 model:
http://www.storesonline.com/site/573683/page/608079
I'm assuming you've got 4 cyl's, 2 carbs, one switchbox, 4 coils. If so, you've got a standard, garden-variety, 4-cyl 66 Cubic Inch motor. Same as an 80hp Merc.
Check out this site for good parts diagrams for Merc & Mariner motors:
http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2
HTH & if you've any other questions about your motor, ask away!.............ed