To answer your question haphazardly: 800Kg, I think.
I have pulled a trailer loaded with 1500 pounds of dirt and 1000 pounds of gravel - NEITHER of which I would reccomend to do except under emergency conditions and along sidestreets. This was done with a 1.6 8-valve equipped with 4.625 dif gears and 30 inch tires.
I also pulled an 800 pound camper trailer to a ZookiMelt (945 miles round trip) and, in the process, destroyed a clutch with 25000 miles on it (broke the center out of the clutch plate).
Don't abuse your Samurai with heavy towing or bad things may happen...