The 3116 and 3126 are in one family, the 3176 and 3196 are in another. No common between the two families. 3126B is a computer engine, very different from the mechanical 3126 predecessor.
All the above engines have their quirks and weak spots, but in a trawler I would not be afraid of them at all. The only ones I have seen that had trouble were in boats where the engines were run HARD. Planing boats like sportfish, Grand Banks semi displacement trawlers with a heavy throttle hand, plowing away at 14kts. Those guys can kill these engines.
Run them modestly, take care of them, and you should get good service.
I also find them to be low smoke, efficient, and generally have good manners. I like their sound, too.