My 81 el camino's differential gears are grinding. I've never done rear end work. From what I've heard it sounds like the spider gear because it only grinds when turning left and somewhat while driving straight, but no grind while turning right. Instead of replacing the gears I've been considering replacing the whole rear end. What other models are interchangeable with the el camino in case I have trouble locating an el camino to pull off of?