Is this stamped in, or on a tag? Sure this isn't part of the VIN?
Used to be that GM put a tag on the passenger side rear of the trans, with a 2 or 3 letter code on the trans (Like CQ) first letter being the make (Chev in this case) and the last being a relative strength rating, "Z" being the theoretical strongest, "A" being the weakest.
I have no idea how GM identifies the individual components inside, it IS likely there is a number on the tranny somewhere (sticker on the trans?) that helps them identify the internals.