When your tightening it up just do it bit by bit, don't do it up completely or you could flatten the diff balls a bit, as it starts to feel tight hold both outdrives( i usually stick 1 side in a vice) & stick a allen key through the other side, then try & turn the centre pulley, if you can turn it it's to loose, just tighten a little at a time till you cant turn it, then your diff is set sweet, check it's still tight after your first run, when the car is assembled i think the diff should spin for no more than 1 second then stop, works nice for my car
Also loads of black grease on the thrust balls so they stay in place when you put them in the outdrive
Hope that makes sense
Gainsy