1972 GMC Sierra Grande truck. First, determining wether or not it's a 10 bolt, or 12 bolt is to count the bolts around the ring gear, right? It's got 3.08's. I want 3.73, or 4.11. Is it better to find some in another truck, or to order some, and have them installed. Either way, I have no idea how to order them or what diameter the ring gear is. Another thing to think about is, I need this to be done quickly because I drive this truck daily.