I agree that the Yanmar crank designed for that purpose *ought* to work just fine. It still makes me nervous, though.
Actually, it should make you nervous. Hand cranking an engine requires knowledge of technique - body position, the way you hold the crank, and how you spin the crank.
I forget about these things because I was taught how to hand crank engines from a very young age by my grandfather. OK, so I'm old, you can imagine my grandfather was a lot older, and lived through the dawn of the combustion engine. Of course the early engines were pretty finicky...
I think an option might be to get a second hand crank, modify it so you could run that modified hand crank with a drill. That way you still have to proper connection to the engine.
Also, thank you for bringing this up. It's a really important point...
dj