Van kept sucking away radiator water until one day water poured out the weep hole, the pump shaft seal, and the rear pump plate seal. Old pump came out fairly easily, but getting it back in was another matter( the water pump bolts need deep sockets, and the belt tensioner needs a big breaker bar to move it). Ultimately I found it easier to put it in from the top, although a guy with a creeper, a rack, and good arms could get it from below. The parts guy said that the water pump, the upper radiator hose, and the serpentine belt were the ones it had when it left Detroit in 1994, so it didn't owe me anything.
Buy the GM dealer's manual for this one, not the one the parts store sells. Plenty of them come up on eBay. Be advised that even the dealer manual leaves things out, like the precise location of the fuel filter. Invest in at least a 3-ton floor jack and four heavy jack-stands if you are going to do much work on this vehicle.