Hmmm...
Here's what the GM PC says..
If you have the ORIGINAL water pump use...
INLET, W/PMP(USED ON PUMPS WITH CASTING #12562459)(INCLS INLET, SEAL, THERM0STAT, VLV, RETAINER)(IF WATER PUMP HAS BEEN REPLACED BY 2004 OR NEWER PUMP, MUST ALSO USE -2004 OR NEWER INLET.)(ACDelco #15-10412)
This...