I've just got around to reading your site. Very interesting and very plausible. Nice one.
A question: Is your 900 yards based on one team doing a days work or just the distance covered by one 'step' multiplied up? i.e. if there was a shift system with untired people could they go further?
Another question: (only just thought of this one) could this method move a large basket of cairn rubble faster than a whole wodge of people carrying lots of small baskets?