The game's keydisk copy protection must be cracked to run it in DOSBox, but the existing TDT crack does not eliminate dependence on the floppy disk controller (because it didn't have to). The attached patch program will remove the FDC dependency, and it can be applied to original files or on top of the existing TDT crack. Run the program in DOSBox where the game is installed. With the patch, and the help of the TDT trainer, I was able to reach the end of the game in both DOSBox 0.74 and SVN. I used the machine=vgaonly setting because some messy graphics are hidden by video blanking as they would be on real VGA.
Edit: Improved the patch to remove all calls to INT 13h, won't access the floppy drive at all. Also fixed two glitches caused by the TDT crack where the level 3 boss graphics were messed up and the level 4 exit portal did not appear after defeating the boss (although you could still exit by walking left).