Within the past month or two I saw some reference (seems like it was an Ariel related place...?) to a motor like the Honda/saildrive-enstein, but it was made back in the late 60's/early 70's, used an Evinrude 2 stroke on the top end. Sailing Uma on YouTube have fitted an electric motor with a saildrive type unit, it was/is manufactured that way - and I imagine more pricey than even a well-kitted Ariel without one would be.
I'm selling my Merc 6hp 4strk to a fellow who needs to get a Catalina 30 down to Florida. A friend was given for free a Yamaha 4hp 4strk longshaft earlier this year; he in turn gave it to me. Great friend! (Note to self: get him a good Xmas present...) It's an older model, he was told it had been barely used. When I went to service it the oil was still golden in color, so I think it has been run less than an hour. I'm gonna give it a break-in treatment, and it'll become Katie's aux. The 6hp worked fine up until 20+ kts wind, I think the 4hp will work for someone like me who likes the idea of motorlessness but it too chicken****e to actually go that way. And the long-term dependability of Yamahas in saltwater environs is not a factor to be overlooked.
One note on the Yam 4's - of all the years they were made, it seems, there were but 2 years when a carb swap could turn them into a 6hp motor.
Mine is one of those two years, that's the only 'bad' thing about it.