Note that Steam GatEB is exactly the same engine as TSS (5.1.0.6545), rather than the standalone GatEB's 4.0.2.112.
So the DLCs being attached to GatEB has no real impact (unless of course you don't own Steam GatEB yet), and Steam GatEB will play any user-made hold, including those built using TSS.
Also note that if you originally purchased GatEB from Caravel directly, you should be able to get a Steam key from:
http://forum.caravelgames.com/member.php?Action=purchases
[Last edited by Tuttle at 09-21-2021 12:45 AM]