Gary,
There is a Gamefisher Model Number but then there is also an engine model number. That model number should be visible on the powerhead. The carburetor may also have a tag attached. These numbers might help you pin down the year.
Depending on exactly what parts you need….the engine model number may be all you need.
There are some very good Tecumseh Service manuals available as PDF. Let me know if you need a copy.