8 3/4 posi unit change

Then I would lose the Sure Grip.....which I would like to keep. The 3.91 (installed in the car) has the sure grip, the donor rear end with the 3.23 does not. I've not taken either of them apart yet, just inquiring on doing this. To be honest, I've never taken changed a set of gears before, so this is new terrritory for me.