First of all I introduced the larger American trucks to towing Bushtrackers with my F-350 full import, before the Ford Australia trucks imported the Brazilian built Ford with the weaker 4R100 transmission.. I solved the transmission problems with an external transmission oil cooler instead of the mesh in the bottom of the radiator cooler that plugged up, and pioneered the use of Transmax Z synthetic transmission oil, all of this nearly 20 year ago.. I have more experience on back tracks with the American trucks than most and I disagree with it being "too big".. Landcruisers do not run on rails, and their wheel tracks are a meter wide on each side. The American trucks are not that much wider than the Landcruiser. I think in the 99% of practical time, this is an Urban Myth from people that have not owned them.
Now I just went outside with Stuart and measured a 200 Series outside to outside of front fender, at 1960 mm. I went over with Stuart and measured outside of front fender to outside of front fender on my Dodge Cummins Diesel 2500 and it was on 2060 mm.. Case in point, only 100 mm difference between them? And when the Landcruiser wheel tracks are a meter wide where they wander all over??? This whole thing about being too wide is an "Urban Myth" from people that do not own them... Their loss.. !!
As to the payload?
It can be varied up and down by the people that do the conversions with their Engineers and a Mod Plate. Much of the time the 2500 can go all the way to the 3500 loading, with just air bags inside the existing coils. I have varied them all, down to regular Car License with a small move down in GVM, and up in GVM with Air Bags inside coils, and air bags over rear springs in some cases for towing larger loads like goose neck horse floats. A lot of the vehicles have the same running gear for the 250-350, and 2500-3500, just a stiffer suspension in the rear. They do not change radically until you go to larger diffs and dual rear wheels, most run the same running gear in the SRW (Single Rear Wheel models).
Kind regards, from the Guy that does the R&D on tow vehicles. I have owned a dozen in 22 years, half Landcruisers, half American trucks, still own one of each as we speak... On the Road with the Ranger