I beleive that car comes with a northstar engine if it does the pump is on the right side of the engine driven by a small belt from camshaft pulley. a northstar water pump socket is required to remove pump properly. the pulley doesnt come off
I agree with 773mtech, I have the same year and model and there is no need to remove pulley. Just the pump housing with 3 or 4 small bolts. Need to be careful when tightening these bolts as it is easy to crack the pump housing. Pump install does require special socket tool available at most auto parts stores to rent or buy. Not terribly expensive to purchase pump or tool to change it. This is a relatively easy job on the 99 Deville with Northstar.