It seems like a lot of effort to just transfer the old geometry over - I think you’d be better off creating modular pieces (using the original geo as reference) and creating the map from that. The pillars in the first hallway, for example, could just be one asset repeated.
Unless you were to figure out an automated method to convert the original map files to something you can import into UE4 (Deus Ex Reborn managed something along these lines) it doesn’t seem like the best process to use.