A lot of old games just had entirely too many untar'd files, so sometimes developers will lump em all in a archive of some type and change the extension to .dat so that noobs leave em alone instead of unzipping them. I tried 7zip ... no luck.
Looks like the header to an archive to me. If I made an archive I would want a list of the files contained at the beginning with index values to where each files data starts.
Whatever archive format was used probably wasn't an old DOS/Amiga era format since the archive change is more recent, possibly GOGs work, so you probably wanna go talk to some people who specialize in stuff like archive formats etc.
At any rate from what it sounds like all versions are probably using the exact same format and you can probably load them all with the port code you already have, once you can open the archive.