gen 3 5.3 aluminum with E stamped on the bare block

[learning LS]

Looking for some help to identify a bare block i picked up.  i found what seemed to be a Gen 3 aluminum LS. (provision for knock sensors at the top of the block) The block does not have 4.8/5.3 stamp, but instead it does have just the 5.3L stamp  on it. Also, the block has an E stamped on it. not even the Machine shop knew what the E meant. it does have a GM stamp on it as well. 

[CamGTP]

The aluminum block in the GEN 3's was the L33. Pretty sure the rest would be stamped 4.8/5.3 for all iron blocks.