I agree re. Yam 2hp. Then Tohatsu/Merc./Mariner 3.5 (or 2.5 if you can survive without neutral gear). Certainly go for a 2 stroke if possible.
If he can't find one then I'd go for the Tohatsu/Merc./Mariner 2.5 or 3.5, 4str. I've got one , as well as the Honda 2.3. The latter is slightly lighter and seems more economical but has a horrid exhaust sound and that annoying centrifugal clutch.