I went last night to pick up a 5.3 and could not figure out if it was a 4.8 or 5.3. The block was marked 4.8L/5.3L, 862 heads. The guy worked at autozone and called a coworker, who was working at the time. According to the coworker, both the 4.8 and 5.3 could have the 862 heads. Is there anyway to tell externally? He claimed it was from a '03 tahoe.

Thanks!

 

There should be a part number on the side of the block that you should be able to cross reference....at least I know there is for the aluminum LS blocks. I doubt it would be different.

 

Unfortunately, this is incorrect. The 4.8L and 5.3L use the same block.

OP: Does it have the pan and all on it? If not, you could cross reference the crank casting number and it will tell which it is (different stroke between the two). That'd be the quickest way to tell for sure.