I projected the Grand Gallery past the King Chamber at the same angle. Yes, it runs into part of the Chamber, but not as much as one would think. If they used the Grand Gallery it would be much easier to continue past the Chamber. What I see, was they were able to move all the stones past the chamber, and only interrupt one key stone. The lowest front stone, and part of a wall which was open at this stage.
Once all the stones were up past this section, then they built the foundation wall that would support that one stone, blocking and removing all evidence of the Gallery path. So why the height of the Grand Gallery. You do not need that height, to pull those stones through, unless it contained the system that aided in the lift.