Ok, found it! Talked to Santa Fe Gelaendewagen importer and dealer. So this is from the horses mouth so to speak!
Rated horsepower for 1980 G 280GE is 73 and the diesel was the only engine he believed was available, which was a 5 cylinder. The correct towing cap. is 1,650 lbs., that's 750 kilograms, for an unbraked trailer and 6,773lbs. with a braked trailer. Without trailer brakes he said the G would not be able to stop.
However, much laughter ensued when talking about actually pulling that weight. He did not recommend it and said you'd be doing about 30mph on flat ground in cool weather pulling that.
He went on to say that the G and Mog are not comparable really for off road use. The G is a fantastic, rugged little truck for on-off road use but could no way compete with a military vehicle in the super rough stuff. Looking at the Mog going across a 6 foot straight drop, 4 foot wide ditch in the pictures we have at http://www.GrannyGumption.com/unimog.htm should be fairly obvious a G or any smaller vehicle would drop nose down into the ditch and need to be winched out because the mogs wheels themselves are taller than the entire G wagen's front end. The Mercedes dealer in Santa Monica where there are quite a few new G500’s said a glaring rebuttal to G Vs Mog; If the G was as good off road for ALL uses like a Mog than why wouldn’t the military and work arenas using the Mog use a G wagen instead of their vast fleets of Unimogs?! Santa Fe said that for nuclear waste disposal in desert bad lands where they live and work is carried out by Unimogs not G wagens’ for obvious reasons. (Basically W.I. Simonson) said comparing the 2 was ridiculous and like comparing a Jeep CJ against a Deuce and a half.
He went on to say that a G will not ford 5 foot rivers or a VISCOUS mud bog going up to the hood. It wasn't designed for it and one would be foolish to use one as such. Obviously the Mog is much higher off the ground both ground clearance wise and approach angle so it's rather silly to say a vehicle lower and closer to the ground could climb up a rock face that a Mog could climb simply because the bumper would smack into the face that the mog would go up and over because of the height. The mechanic said even with a Brabus engine he would not recommend towing more than 2000 pounds with a G. Since these fellas do nothing but sell and work on G's 100% of the time, I'd say they are qualified to end this matter. Bye!