I picked apart some of the Dark Forces files myself as a kid. The GOB file was pretty obvious - I was familiar with Doom WADs, it's basically the same. I figured out the graphics formats by setting up VGA 320x200 mode with the contents of a .PAL file, and dumping the graphics file into screen memory. Then looking at the noise around the familiar patterns to figure out all the run/skip length stuff that wasn't just a pixel value.