Looking around I found there are some significant differences between Kaiser Knuclke, Global Champion, and Dan-Ku-Ga. from what I've been reading the following differences exist:
Kaiser Knuckle - original Japanese release
Global Champion - international release
!-removed super moves
-added character prologues
-change character portraits of Kazuya, Liza and Lihua
-changed title screen
-added "winners don't use drugs message
Dan-Ku-Ga - updated version (prototype)
!-Boss characters (Gonzales and Azteca) are playable
!-added ability to back dash
!-changed execution of certain moves
!-added ability to select difficulty
!-removed ability to select first opponent (except on training difficulty)
!-updated CPU AI
!-third boss (General) can be fought without meeting special conditions
So this is another one where it seems it'd be worth having all 3 game variants available.