Sorry, UB, I'm REALLY late to the game to see this one. Architects usually aren't much help on these issue - - we'd just draw it up, and leave it to contractor's "means and methods" to figure out a solution. LOL
Seriously though, that is some incredible stone work. It helps tremendously that it is sandstone, which enables minute levels of accurate sculpting, provided you have the patience.
We quickly tend to dismiss such precision as impossible for that era... but before we do, think of similar feats of complexity:
1. The precise work of bhuddist monks when they carve entire texts onto a grain of rice, or their detailed "paintings" made of individual grains of colored sand.
2. The metallurgy of ancient swords.
3. The early concrete structures of the Romans, so welll done that for hundreds of years people had know idea how to build to such levels of precision.
I've been told that even in our own culture, some prisoners can go to this level of detail and precision in their craft (the biggest example being body art - tattoos). All it takes is all the time in the world, and unparalleled mental focus, often aided by amphetamines.
The key is a lifetime of patience and dedication to craft.
Think about even some of the everyday stuff that we use, such as a machine screw. How did we ever get to the level of precision that it works so flawlessly?