If you discount the 20 year assumption then it becomes possible to do it with the technology available. Egyptologists cling to the 20 year time frame because they insist that the pyramids were tombs-and-tombs-only. If they give up the 20 years...which is way too long for the average reign of a pharaoh... they would have to give up the tomb scenario. They would rather cut off their own balls than do that.
How long did it take to build the cathedrals of Europe? Centuries and they had far better technology than the Egyptians.
How long did it take to build the cathedrals of Europe? Centuries and they had far better technology than the Egyptians.