Inboard
If you had said that you'd mainly be motoring in and out of the harbor and around San Diego Bay, I'd have suggested that you stick with an electric start outboard. You'd have more than enough power and would sail faster with the prop out of the water. If, on the other hand, much of your time will be spent in the ocean, going to Catalina, etc., the inboard makes the most sense. In the ocean swells your prop will stay in the water better and your transom will be completely closed. You might want to check the archives for the pros and cons of the Atomic 4 vs. a Diesel. With the Atomic 4, you'll have more horsepower than you'll ever need. With the Diesel, you'll have a somewhat safer system (no gasoline) and a simpler engine. It really all boils down to condition. The earlier boats all had raw seawater cooling whereas the newer boats (post 82 or 83??) were built with heat exchangers so that the saltwater never ran through the engine itself. If you can afford a newer boat, the heat exchanger is the way to go. As far as I know, the C-27 was made with two basic layouts, the traditional with port and starbord berths and a fold-up table and the dinette model. In my opinion, the traditional model is the way to go. You have more room with the table up and you have the option of converting the two berths into a queen-size berth by bridging the gap between them (again check the archives). You didn't mention tall rig vs. standard rig. I believe that the tall rig is the rig of choice for your sailing area. You probably won't encounter many boats with a shoal keel, but I'd go for the deeper draft standard keel.
