I can't verify or refute any of those numbers personally. But, I will say that these lifts were usually done in strange ways, i.e. the illustration accompanying the original post. My guess is that is a type of dead lift. The back lift, I would guess is along the lines of what Sandow was famous for. In the original Pumping Iron book there is a picture of Sandow with his back to a flat apparatus, almost like a small floor attatched to a lever or something. Then there are all kinds of people on top. So, he's just kind of holding the weight. This is, of course, about the only way a man is going to "lift" 4000+ lbs. I don't mean any of this to be negative. On the contrary, It is very possible that every one of those lifts might be accurate, but just different in their execution than we might imagine. Very impressive, and a legend of a strongman.
J.