An educated guess is that the Big cylidrical one controls compression damping, the knob at the bottom of the shock controls rebound damping. and the little one with the big knob is a hydralic remote preload adjuster. You can find out for sure by turning the knob and seeing if the silver metal part at the top comes in and out and changes the pressure on the spring.
Thats pretty trick for a mid-nineties Kan-0-tuna!
I vote for you having the spiffiest shock on any GS. Problem is that it probably still has a spring for a 500+ lb. monster on it...