A bunch of workers hanging their body weight on the lever end would raise the stone a foot or two. You prop the stone with some timbers, shorten the lifting rope, and repeat. When the stone gets to the next level of the pyramid, you rotate the lever arm horizontally and pivot the stone to the next step.
Sounds plausible, except how does that lever get the stones to the top of a 455' structure? The widest "step" doesn't seem like it would allow room for enough guys to exert 800 lbs on a lever, much less for the lever itself. And we're talking a pretty long lever by the time you get halfway up. Then, you've got all the limestone sheathing to put up and you have to make sure the inside chambers are there, and accessible..
However they did it, it's pretty remarkable. I got to see it once up close and it's amazing.