Charlie,
Be careful with how much power you put on the back of ST. As the original spec says it can take 90hp, remember that is old skool HP - measured at the fly wheel. Modern outboards are measured at the prop - so a new 90 is pushing out quite a bit more beef than an old skool one. I suspect 75 would be more than enough, plus I don't want to be cut-up by a Family 4!!!!
Rob