The big one on it's side, on the left. It appears to have the correct post configuration for your existing batter cables.

I wouldn't worry too much about the alternator, as you're not going to be using your winch every day. Like you said, you don't have anything else that's going to be a massive tax on the system.

If you decided that you did want to go with a stronger alternator, then a Mean Green alternator would be the best choice.