Well,
The mercury 9.9 and 15hp 2 strokes weigh 75 pounds.
The 1993- 2005 johnson and evinrude 9.9 and 15hp 2 strokes weigh 74 pounds
The 1974- 1992 johnson and evinrude 9.9 and 15hp 2 strokes weigh 74 pounds.
The tohatsu and nissan 9.9hp 2 stroke weighed 59 pounds (I am pretty sure) So if you are looking for the lightest I would look for one of those.