I had the privilege of being crammed into AN2 aircraft being flown by a subsidiary of Varig airlines, called Panair, which leased the planes/pilots/ground crews to Takahashi Mining Corp.
The only structural difference I can see between the planes in the pics and the Soviet built, Brazilian models is the wheels. The wheels on the Brazilian planes were huge in comparison. Very similar to what is often seen on bush planes that regularly land on river banks.
As far as STOL, that ratio definitely changed depending on the load the plane was carrying. Some of the pilots hated flying the plane when it was empty and would fill old fuel bladders with water to add some weight. They could easily dump the water where they picked up their cargo or even in mid flight, just by opening the door and allowing the slipstream to pull it out of the filler spouts.
I liked those planes. The pilots were very professional and didn't take any risks. Yes, boring, but good jobs were hard come by in Brazil back then.
I remember being put down on what appeared to be a solid beach and when I jumped out of the plane, I sank into the mud, up to my waist. The plane, fully loaded sat on top of the muck like an emerging Mayfly.
The co pilot laughed at my predicament, helped me back into the plane and we took off to make another very short landing on a gravel spit in the middle of the river. The barge sent an inflatable over to pick me up.
That gravel spit was only 50-60 meters long and the AN2 didn't have any problem taking off again, even though it was almost fully loaded.
