All the naproxen and cortisone injection will do is maybe help you be in less pain while your body attempts to fix the problem (you probably already knew that). If cortisone is brought up again, I'd say go see the prolo guy (I'd say go see him anyway).
I worked on an AC joint last night with some neural injection therapy, actually. We'll see how it turns out. If it goes well, I'd be happy to share it with you so you could share it with an open doc.