Don't forget the difference in compression ratio between the AMF/BHC and ATL. I believe there are three headgaskets to choose from and marked at the tab. Verifiy which one is used for future referrence.
If the exhaust end failed, fragments can enter the inlet via the EGR. The intercooler would probably prevent fragments entering from the compressor end.Definitely no turbo bits ingested, it broke off exhaust end and made quite a chunky indent on exhaust end housing though, intake side was in one piece with no broken fins.
Can you borescope the piston heads and bores and valve bases? Remove the manifolds to try to see if damage to the upper ends of the valves. You are 100% sure the belts are correctly timed and the belt does not have any damage? My early suggestion for the compression check and other damage to the engine when the turbo failed is looking stronger all the time.