Back when I bought my 1992, it had new a genuine Ford water pump when got it. Records said only two since new and I think it had about 240K when I got it. I generally settle for the aftermarket junk as it's generally "good enough", however, I would put the IDI water pump on the "OEM if you can get it" and "it's OK to pay more for it" list. I have no idea how or why it should be so difficult to keep a seal on a shaft, but the aftermarket ones don't seem to last very well. You could also think about changing the belt tensioner and idler while you have it apart, but I'm pretty lost on the tensioner, as I feel pretty strongly that the factory ones are **** (both styles: shock, no shock, I have grenaded both of them)
Make sure you cut a piece of carboard to cover up the back side of your radiator, I think there's one bolt that longer than another, I always try to keep track of exactly what came out of what hole, other than that I think it's pretty straightforward.