I just had a poke with DosBox, memdump etc. The first level tilemap was clearly visible in memory, so I guess I was looking at A1CHAOS.PLD. On inspection, looks like endian swap which was expected. Plus there is also some extra data and what appears to be slight differences in the data, so maybe tile index changes. Attached is the PLD from memory. I'm assuming PLD=PC Level Data?
Was there a PC demo for Chaos? I'm gonna go looking.. I can extract some files from CHAOS.DAT if needed, but they won't be decompressed, that still needs to be figured out..