[Player Lin]

The maindata in that ROTT TC with ZDooM engine is rott_tc_full.pk3.
(zdoom.pk3 is core data file of ZDooM source port, not needed at all.)

And it's DooM format from ripped ROTT resources, of course, didn't used any of original ROTT wad data at all. I don't know XWE can open PK3 or not, I don't like it when it already stopped updates and out-dated for newer DooM maps/mods/TCs.

(The PK3 files actually a zip file, you can open it with newer WinRAR, but its data has some DooM binary format. Sprites and sounds are PNGs and WAV so you can just extract them out but I don't know they're works or not with this way.)

Or you can.....

Try get SLADE 3 on here.

And if you want, try get latest SVN Builds from here. Extract the package to your SLADE 3 installation(install it first) and overwrite them.