The vast majority of Dana 60 rears will need the spindles bored. There are a few that came with 30 spline shafts and the larger bore, and there are even fewer Heavy Duty Dana 60's that came from the factory with larger bore spindles and 35 spline shafts. Look for a double ribbed housing if that is the route you want to go. I hear that many people will cut the spindles off and replace them with Dana 70 spindles that already have the larger bore (1.650", I think?)