Interesting. I suspect that the original engine has been replaced with the Yanmar. I've seen that happen more than once. I'm just surprised that they would have retained the 3/4" shaft. Most opt for the standard 1", having to replace the strut and stuffing box. Most mechanics suggest that the 1" shaft is need to handle the extra torque of the 18 hp. But then, I've never seen a shaft bent due to the extra hp of a new engine. I've actually thought of going to a saildrive when I replace the old MD7A. It'll be easier to install and reduce the vibration at the same time. We'll see....