I was hoping for someone that really knows how it comes apart to answer you.
i just wanted to make sure they knew what motor you were asking about.
But with that said, it has to be attached some how, as it was not cast or machined whole..
it is not welded that I can see.
so it has to be screwed on.
Just my opinion.
If I was you I would google Rodbolt17 and see if you can get him to answer your question on the forum he posts on now a days. He is a Yamaha Master Tech