Okay, looking at this axle I am now considering swapping for a rebuilt complete drive axle. Looks like there's three options:
4x4, semi-floating (9.5" ring gear), 3.42 axle ratio (opt GU6)
4x4, semi-floating (9.5" ring gear), 3.73 ratio (opt GT4)
4x4, semi-floating (9.5" ring gear), 4.10 ratio...