Well... The info up on Wikipedia is not entirely accurate. The games use the same overall level structure (square/tile-based). The engine was just redone in Watcom. Watcom 9.x had some odd requirements in how it dealt with certain things, inline assembly language most notably (through #pragma's. A real annoyance compared to Borland or MS's C++ compilers) and memory management (straight malloc's via flat-memory model rather than needing to use EMS (which must be set up in the autoexec.bat/config.sys on a straight DOS system. DOSBox enables these by default) ). They just carried the capabilities (much) further after getting the engine going. There's info released on the internal data structures of both the Underworlds and SS1. There's a lot of overlap in those structures.
Post edited September 22, 2015 by Firebrand9