Like previous replys stated, bolts on the motor are metric.
My '03 Yamaha F225 is the first Japanese boat motor I have ever owned, and aside from impeller / housing change and the basic maintenance, I haven't done any other wrenching on it (though timing belt change won't be too far down the road). However, I have done alot of work over the years on Japanese motorcycles. From my experience, one piece of advice I could give you is to use a torque wrench religiously. Particularly when tightening a steel fastener into threaded aluminum parts.
