Look at this on my phone earlier and didn't feel like typing much on there. Anyways, like I said earlier definatly 3.73's. As others have mentioned, definatly open diff on the front. As you already mentioned, the rear is welded. However, those welds don't look the greatest specifically on the upper side of the carrier to spider gear weld. If it were me I'd run it till it broke that way, but I wouldn't push it hard it you want it to last.