Engine Casting Help

[chevyboy214]

I have decided to replace stock my 5.3l out of my 2004 Chevy Avalanche after having a boat load of problems with it. The casting number on it is 1256392. I have recently purchased a upgrade engine from a company who takes that block and strokes it to a 5.7l with other upgrades. The problem im having is nothing is fitting. The knock sensors are on the side now instead of on the top (knock sensors also will now screw in hole is to small) and the oil sensor wont screw in. (same problem hole is to small for the threads.) The is block stamped (4.8 5.3) and (gm) and the casting says 12576177. I cant find this number on any gm site or web posting. Can someone help me out?

[0rion]

I never have good luck finding block part numbers.....can be tough to find. Sounds like a Gen IV 5.3L though.