Thanks everyone!
Well good news - ish~ After sending pictures and videos to Chevy I just spoke with them and they advised to proceed with installation. We are 99.9% sure that the chunk is from a broken valve cover filler spout. The oil filler was clearly knocked off at some point and the valve cover broken and replaced, but obviously the broken wasn't recovered until now.
They did give me the option to go ahead and send it back to them but it would require putting the motor back to stock configuration. Even if there is a problem it is under warranty so I can send it in later, plus I they mentioned that the warranty may also cover part or all of the removal & reinstallation of the new motor. So it would definitely suck if there is a problem but I think we will be ok.
sooo BACK TO WORK!
J