90% sure he means "largest manufacturers of marine engines" rather than "manufacturers of the largest marine engines". If I'm right then the largest mfg probably produces smaller engines since there's so many more small boats.
Yeah, seems like all you see anymore for I/O engines is Mercruiser and Volvo, which do indeed use automotive engines. I'm not sure if there are even any other manufacturers left.
I'm less familiar with outboard engines, and I don't know what is more common (I/O or outboards) for recreational boating. In the Great Lakes, I/Os appear to dominate, but I've noticed that videos of boating in Florida and the east coast show a lot of outboards even on the bigger boats.
FL, especially in the Gulf, has mostly outboards because it's so damn shallow so it's nice to be able to pull them up when you're really tight. And lots of pontoon boats in the intercoastal.
