Avalanche Waterpump Help

[theblackbeast2]

I need to order a water pump for my 2004 Chev Avalanche and need the part number to order

 

I am ordering from rock auto and when I search for the part I was going to get the AC delco but it give me 2 options

ACDELCO Part # 252845 {#19195104} Cast Iron Impeller; Does Not Include Mount Bolts; w/ Gaskets

ACDELCO Part # 251714 {Click Info Link for Alternate/OEM Part Numbers251616, 251706, 88894290, 89018166} OE Design; Stamped Steel Impeller; Includes Mount Bolts

 

But when I go to the ac delco website and put my vin in it say I need part # 251-743 which is different from the other one and say it need

ACDELCO Part # 251743 {#19256261} OE Design; Stamped Steel Impeller; Includes Mount Bolts MUST ALSO ORDER 12600172 INLET & 11516480 BOLT

 

So which one do I order, need to order today

Also which belt do I order for the serpentine belt the one for the 105A alternator or the 145A alternator