You can buy one here http://www.iboats.com/Mercruiser-St...3115177--**********.924109276--view_id.373439
Or you can view one on line here http://boatinfo.no/lib/mercruiser/manuals/mercruiser10.html#/2 for the engine and here http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/2 for the drive.
That is a good well proven drive on the old GM iron duke. A hard combination to beat. I'd do the basic maintenance - oil changes, tune up, belts, water pump service, check the hoses and maybe a thermostat - and then see how it works.
Those manuals do not call out my serial number on the engine. Is there one out there specifically for my engine? I want to make sure I have the exact manual prior to break down and rebuild.