Maybe nobody else has had this minor annoyance, but when I recently replaced the alternator belt on my M35b engine, I found the belt I'd bought was the wrong length. When I took it back, the guy in the store showed me his book - the parts book listed the wrong belt. It's an annoyance when you have to run back and forth to the store when you're in the middle of a project, but if you're out at sea and your belt breaks and you think you have a spare, but it's the wrong one, it can be more than an annoyance.

I'm just mentioning this for others with the same engine... It might spare you some time or even more than that.