Well not that this will help you a whole lot but i think it points more in the direction your getting at, and i don't have a water pump to look at right here so anyway i looked up the pump in the dealer parts program and there were at least 2 different pumps on the gen 1 4d56 engine md997150 being the early version and md997618 newer version which carried over to the gen 2's till the end of 92. maybe you need to head down to the parts store or junkyard and do a little on the spot comparing. i also looked this up on rockauto and they sell 2 different versions of the pump depending on year aswell so there is something to that.