It looks like it's better to order one with the zero stop to start with ($100) otherwise it's $220 on the factory service form to change an existing scope which seems a bit steep.
I sent mine back a few months ago and had the zero stop installed and it $215. It is nice to have but I hate that the zero stop does away with the turret scale. Not that it is that big a deal but if loose count or your not sure you have run the turret all the way down and start all over to know how many revolutions that you have dialed into the scope. I think it would be nice to have both.