As a vetern swimmer with passed shoulder issues my advice is get a Physical Therapist if you don't have one...and kick in the pool with a kick board and without. It will help a lot and doesnt require you to pull.

I would focus on strengthening your shoulders for March and April for sure using resistance bands (be cautious with weights). By using bands you can slowly build up the strength needed in the shoulders for swimming. Here is an example of some simple and standard band workouts for the upper body but a great place to start.( http://exercise.about.com/cs/exerciseworkouts/l/blbandworkout.htm)

The swim itself it is great because of the westward current in the bay pushing you to the golden gate bridge. Go to the pre-race swim briefing for sure to get tips and get super fired up.

Race smart and safe and enjoy the views, they are incredible!