I would think that spanning your two 24" studs with a 3/4 plywood panel and mounting the bracket to that should work, certainly for a 42" plasma. A 50", I'm not so sure.

If you've read enough of the forum you've seen us say again & again; hire a pro. Have you considered that? You already own a bracket that you're not wild about; any reason to possibly get in deeper and still not complete the task?