I measured pinion depth on my existing 2.56 gears and matched that on the 3.42 gears. I matched the crushed pinion length as well. Stake the pinion nut and use blue lock tight. I used the feel method, you basically want the pinion bearings as tight as possible without dragging, spinning by hand. Spin your stock pinion once you get the ring gear out, you can tell the feel. I had used gears both times which I think are much more forgiving, kind of like a used camshaft and not much of a loss in you go wrong. My next 8.5" Type O gear swap in my 1970 Cutlass S will be $1000 in parts. Thinking I better get the holding tool and magnetic base with dial indicator. I am pretty sure I have a new inch pound torque wrench as well. I will get the bearings pressed on and I will get a brass punch to put in the races. One nice part about that rear is the bolt in axles and the aftermarket posi allows Moser corporate 8.5" 10 bolt in replacement axles which is a bonus, price wise.
