I missed dark forces first time round, but picked it up on budget back in 1996 and had an AMAZING time with it.
But Dark Forces, jedi engine, always had this gut wrenching perspecitve skewer when looking up and down - especially with the skybox doing it's own thing.
For one of the doom GZ GL z doom, I forget which one,
They actually compensated for the perspective skewer so the world rendered as expected with say a modern day engine. (more than likely by importing and converting the level geometry into another engine all together.
Now that you have mouse-look, high resolutions, I find the faithful perspective skew when looking up and down really stomach churning.
So if possible, I know it's not just a simple thing, but could you possible at all fix the perspective problem - Tall order I know, I haven't seen the dagger fall stuff yet if this is an issue there or not. I don't know if this is already on your own todo list, and I don't mean to be of great bother.
The weird perspective distortion you describe is a result of Dark Forces not actually being 3D. It may look 3D, but it's actually using a technique called ray casting (you can google if you'd like to see how it works). Suffice it to say that ray casting does not actually support real, perspective correct looking up and down. The effect is achieved in game using fakery.
This issue is not shared by the various redone Doom engines because those use actual, real 3D rasterization. XLEngine will be real 3D, so it won't have this problem unless our overlord deliberately recreates it.