yes the pump boss is cast into the block but the passage for the fuel pump push rod to reach the cam is not machined.
1253020283 are both based on the 1996 - 2000 truck blocks, which do not have a provision for the mechanical pump machined into the block. The earlier center bolt head one piece rear main motors had the machining done for the fuel pump push rod, but as time went on they no longer machined for that because because carbs were fazed out. Also that motor may or may not have a provision for a mechanical fuel pump.
