The GFX in the game is not compressed but stored in a unusual way.
A description for this can be found here:
Also because of this script, we know the exact location of each sprite in both roms.
The offset information can be found here:
With the provided offsets I was able to copy a bit GFX over for the brown soldier and got this:
Unfortunately after this it crashed.
Now I am searching for somebody who is interested in looking into it and write a little tool
or script to swap assets into the final version.
The uncut project is already going on here: