Just had a friend give me a very obviously old mercury outboard. said he thought it was a 25 hoarse but didn't know. The serial number tag just says MARK 28 (blank) serial number 1163077. Can't find it on mercury's serial # search. Little twin cylinder moter, doesn't look big enough to be a 25, maybe a ten? Just from the look of it it may be from the 40's or 50's. white lower, brown or black upper(pretty faded) Any help would be appreciated. THANKS