The IMO under-discussed idea about the 'doors' is that they must have been designed into the pyramid. I've read a few explanations that the copper attachments were fixed to a pole or rope and used to either push or pull them into position in the shafts after the construction was completed.
In my estimation this explanation is completely infeasible.
As you should well know, the shafts do not run straight. They bend almost immediately from the interior of the chambers up towards their angle. Therefore, they were not used to lower the blocks into place from within, unless the AE had advanced pipe-fittings and pipes of considerable length that were stronger than copper to a point that the difference is enough to carry the weight of 2 tons (average weight of block in the GP.)
I haven't ran the math on that, but I would say you would need a very, very strong metal indeed. I mean, what is the length? 200 feet? More? to hoist DOWNWARD from two points a mere couple of inches apart?
Lowered into. No.
Same problem, except it must be rope. Still yet, I doubt the structural integrity of those tine copper handles can hold up to the force of 2 tons bearing down on them. Nevermind the fact that the blocks wouldn't form a seamless fit (in reality I'd give odds they do) because you would have to cut the rope from above to free the block.
In any event, the mass of the block itself would warp the handles no matter the method of placement...
These handles are simply a puzzle.
Or serve another purpose.
As a conductor perhaps.