Years ago, the Smithsonian proved that, with the use of only eight pieces of wood, large stone blocks could be easily moved with just a fraction of the manpower. They do this by forming two wooden "wheels", held together with pins, which turn the rectangular blocks into cylinders.
To build a pyramid, you first lay the bottom layer of stones, and then you pile dirt around them to form a dirt ramp that you can then roll the next layer up. Eventually, all but the top of the pyramid is covered with dirt. And when it is done, take away the dirt and there is your pyramid.
Dirt ramps were long since used in the region. Perhaps the most famous example was the giant dirt ramp used to attack Masada, in AD 70, by the Romans--far larger and more complex than anything the Egyptians would have needed.
Now if things were so relatively easy, compared to the traditional model, at the pyramid site, it would also explain why the quarry and stone carving cities have been found, but no equivalent giant slave city to actually build these same pyramids.
As far as the concrete blocks, I would think that when making the majority of the pyramid, the blocks could be somewhat irregularly sized. However, for the final outside layer, you would want them as regularly sized as possible--hence molded concrete blocks, for aesthetic reasons.
The reason that such blocks only seem to exist at the top of the pyramid can be explained by the fact that many of the lower blocks were long ago looted for other buildings.