Source: https://dukeworld.com/classic%20dukeworld/tc/doom/doomduke30.zip

Steps:
* Unpacked doomduke30.zip, short of doomduke.bat and Doom.ico.
* Renamed doomgame.con to GAME.CON.
* Unpacked DOOM.GRP with kextract and then deleted DOOM.GRP.
* Deleted the following DOOM.GRP files which were already in doomduke30.zip:
DEMO1.DMO, DOOMDUKE.BAT, DOOMDEFS.CON, DOOMDUKE.RTS,
DOOMGAME.CON, DOOM.ICO, LOGO.ANM.
Also deleted DOOMUSER.CON, KEXTRACT.EXE and KGROUP.EXE.
The GRP's DOOMUSER.CON differed from doomduke30.zip's
by not yet having episode 3's map names changed.
* Created a new archive from the available contents.

Note that doomduke.rts was preserved but wasn't renamed to DUKE.RTS.
Hence, like the original release, it isn't expected to be used by default,
unless you use a source port modified to do so.