Pontiac Repair: Firebird 2.8 water pump, auto parts store, motor model

Question
I bought an '85 firebird 2,8 and my water pump has gone out. The engine had been changed and the bolt pattern on the '85 water pump I bought doesn't line up. How can I find out my motor model year?  

Answer
what i would do is this  remove the waterpump from your car and take it to the auto parts store and see if they can go back or forward a couple years to see if they can mathc it up for you, or you can go through the trouble of trying to find the engine seriel number and match it that way to