One could argue, I suppose, that the plug was slid down the ascending shaft first (before the granite plugstones, obviously) and wedged into position. After that was accomplished, then sliding the plugstones down would have finished the job.

I personally think that is problematic, because if they had a problem with the plugstones getting wedged in, they would not have been able to ease them along to their final resting place from below. The fact of the matter is, though, it may not have been necessary. They were far more experienced at dealing with large stones and weight than we are, and they may have known that a simple coating of cow fat on each of the four walls of the AP was enough to keep the big blocks of granite sliding down.

Also, in your diagram, you show the block to be the full size of the current opening. Do we know this is actually the case? Could it not have been a simple flat stone, perhaps 12 inches thick, that was just pushed up and wedged into position like a big flat door?

Anthony

You can lead a horse to water but you can't make him think.