Sorry for the late response, been away for a bit.
That is a 1988 Sears (branded) Gamefisher twin cylinder 9.9 horse that was built by Force and tagged for Sears.
So essentially a 1988 Force.
Force was the engine division (US Marine) of Bayliner boats. They had bought Chrysler outboard when Chrysler marine went bankrupt and rebranded the motors as Force making very few changes. Then when Brunswick bought Bayliner, since Brunswick owned Merc already they gave the Force line to Merc. They continued the models for a few years - some were mostly old Chrysler designs/parts, later some were cobbled together contraptions that had both Chrysler and (mostly) discontinued Merc parts and then there were a few that were pretty much pure Merc parts but typically from discontinued models so these were an easy way for Merc to use up parts that were no longer in great demand.
Force was always a more "cost effective" engine option and typically had (technology) older than their actual model year. They were functional motors but could be challenging to find parts for - there was one model year where a single horsepower had 30-something "sub-models" - when they ran out of one part they just found something else that would bolt on and kept up production until they ran out of something else and then swapped something else in - a real "franken-motor".
I have no experience with the smaller Forces such as this so can't give any opinion on your particular model. If it's running I would treat it as a disposable asset. I don't know where you would get routine maintenance parts (try a google search). While Force made this for Sears they didn't produce the 9.9 under their own brand name for a couple more years (after this one) and each of the years (they) branded the 9.9, the parts lists are quite different.
