I've read about that door and mostly remain impressed with the fact that the door itself is very massive and therefore extremely challenging to work with for one man. But if we presume for a moment, that it was possible he could have done it with predictable less mysterious means, then I'd like to try my hand at an explanation.
If I managed to get the rock over to the spot where it was put in position, then if I were to attempt to do what he did, the following is what I might do:
Orient the rock flat on the ground with the base of the rock at the point it is to be stood up on. Stand it up with the tripod assembly, with some bracing at the base so it wouldn't slide out. Get it stood up as close as possible to its balance point with lose bracing so it can be adjusted vertically around that perfect balance point. Find the point at the base where it sat and measure out from that point horizontally to a point that vertically would be clear of the sides of the rock. Plumb bob from that point straight up to a point horizontally parallel to the very top of the rock. And then use that bottom measurement to measure in to the point, just above the rock, where the top of the hole should be, to create a perfectly vertical vector straight down to the point it now sits.
You then have the base of the rock where it sits established, as well as a point perfectly plumb bobbed directly above that point. I would then carefully shift the rock within the lose bracing that holds it up until I found a point that was as close as possible to the point where the rock took the longest time to fall out of balance and tighten the bracing to hold that rock in place. This should then be where the rock is as close as possible to a perfectly balanced point, with two points marked off determining the vector of the drill hole.
Above that top point, you could plumb bob a perfectly vertical vector which could be the steel pipe shaft of a tube drilling bit mounted on the bottom end. If you have greased brackets near the top and bottom of that pipe shaft, allowing some downward drilling space, you could hypothetically drill straight down that original perfect vertical vector that follows the perfect balance point of that rock. The drilling would have to be done in increments that allowed for pipe section extensions to be added the deeper it went, but it wouldn't have to compromise the tensile straightness of that pipe because it could contain an inner pipe to keep the straightness from being compromised.
Something like that. Sorry for no diagrams. Is it understandable?
It seems like an explanation that would sufficiently be considered a viable answer for how he might have done it without any advanced magic, IMO. HOWEVER, I'm convinced from all the rest of the full story and all the things he's done in the time it took him, and all other curious eye witness accounts, that he DID quite possibly have a 'magic' tech. So I only raise this point to explore the possibility that reliance on the existence of that door may not be sufficient evidence to convince one of his 'ability'. If I see a potential straw man argument that a debunker drools over and uses to dismiss, I'd rather beat him to it and remove it from the relied upon list of corroborating evidence.