Oh yes, it is an extremely labor intensive process. Especially with the state of the stock Miata cylinder head. The processes used in manufacturing this head seems ancient. The sand casting is very rough. Compared with Honda heads, ours needs much more grinding and only after can you start polishing. With Honda heads, not much grinding is needed.
No, I didn't do my own work. This work was done by a friend who belongs to a family of racers with their own commercial machine shop. He does this kind of work all the time. And the work is partly science and also partly art ... very difficult to describe. Also, this is the kind of work that you can't do yourself without a machine shop. Take a look at how the valves were unshrouded. The cut around the edge of the chamber to open up the valve is something that you can't do at home - that has to be done by a machine.